This rank list may not be what you're expecting.

If you're looking for something that prioritizes projected output and long-term impact — standard rankings, basically, but with an emphasis on youth — my top 100 dynasty rankings are more your speed. If your league is more prospect-driven, on the other hand, my top 100 prospects are due out in January.

Rest assured, your needs will be met.

This list is my chance to serve someone else — an owner in a different sort of keeper league, but one that's plenty common in its own right. I'm talking about the kind of league that allows owners to keep a player relative to where he was drafted last year.

Roster turnover is oftentimes greater in those leagues, with owners maybe keeping just two, three or four players. Sometimes more, which is why I don't want to completely neglect the long-term aspect, but it's of less concerned here than in the dynasty rankings. The goal here is more to capitalize on the immediate value afforded by the format, stowing the best bang-for-buck players so that you can lock in that advantage for another year.

The calculus isn't quite that simple, of course, since the advantage only matters to the extent you believe in the player. And if that advantage carries over year after year, as opposed to just once, your belief in the player becomes even more critical.

It can never be one-size-fits-all, can it?

No, it can't, which is why now seems like a good time to point out that all 50 of these players, as well as others using the same contingent-on-2018 criteria, are good keepers, meaning ones you should be excited to keep, if to slightly varying degrees. The list, then, is more to help you with close calls or even just talk you through the process (since chances are your league's values don't align exactly with ADP). Not gospel, in other words.

But fun, right? Can I get an amen?

Note: ADP is short for average draft position and refers to where the player was selected in 2018, assuming a 12-team league.

Top 50 keepers for 2019
Mike Trout Los Angeles Angels CF
H2H ADP: Round 1 / Roto ADP: Round 1 / Age: 27 
He's the most consistently studly player in Fantasy Baseball history, the guy everyone would take first overall, so there's no way to get him at a discount, really. But once you have him, you never let him go.
Mookie Betts Boston Red Sox CF
H2H ADP: Round 1 / Roto ADP: Round 1 / Age: 26
Mookie Betts is nearing Mike Trout levels of assuredness, excelling at everything with no potential pitfalls in sight. He's the sort of asset you could always cash in for bargain keepers should the need arise, but with as many years of studliness as he has left, it probably won't.
Jose Ramirez Cleveland Indians 3B
H2H ADP: Round 2  / Roto ADP: Round 2 / Age: 26
Jose Ramirez joined Trout and Betts in 2018 to form a Triforce of superstud hitters far surpassing all others, so keeping him for anything less than a first-round pick is a no-brainer. He doesn't feel as safe as those other two, but only because he keeps blowing the lid off the ceilings we assign to him. 
Alex Bregman Houston Astros 3B
H2H ADP: Round 4 / Roto ADP: Round 4 / Age: 24
The strides Alex Bregman has already made by age 24 set him up to be an MVP-caliber player for years to come, and you bought in just before everybody recognized it. I mean, more walks than strikeouts? An improving fly-ball rate? He's your centerpiece, clearly. 
Francisco Lindor Cleveland Indians SS
H2H ADP: Round 2 / Roto ADP: Round 2 / Age: 25
Francisco Lindor maintained his power gains from 2017 and finally started to run a little, too, cementing his place as the new top shortstop in Fantasy — and with at least another half decade of his prime still to come.
Ronald Acuna Atlanta Braves CF
H2H ADP: Round 10  / Roto ADP: Round 8 / Age: 21
It took a few months for him to hit his stride, but Ronald Acuna ultimately lived up to the preseason hype, zooming past all rookie challengers in August and September. There are lingering questions about his strikeout rate and stolen base ability, but this is a discount you can't expect to see again.
Juan Soto Washington Nationals RF
H2H ADP:  Undrafted / Roto ADP: Undrafted / Age: 20 
Presumed to be years away at the start of 2018, Juan Soto went on to have arguably the best season for any 19-year-old in history. A potentially power-limiting ground-ball rate gives me some reservation, but longtime Fantasy Baseballers have probably fantasized about going back in time and locking up a 21-year-old Albert Pujols on the cheap. This could be that chance. 
Vladimir Guerrero Toronto Blue Jays LF
H2H ADP: Undrafted / Roto ADP: Undrafted / Age: 20 
Sure, we have yet to catch a glimpse of Vladimir Guerrero in the majors, but it hasn't stopped people from taking him as early as Round 3 in standard redraft mocks this offseason. So the discount for those who managed to stash him away is already enormous, and the upside ... well, he's the best minor-league hitter I've ever seen. 
Manny Machado Los Angeles Dodgers 3B
H2H ADP: Round 3 / Roto ADP: Round 2 / Age: 26
A one-year blip in 2017 may have allowed you to snag Manny Machado at less than his usual first-round rate in 2018, and in the right format, it's a joy you can live over again. That 2017 season wasn't even all that bad, all things considered, and the three surrounding it are like a dream come true for a shortstop still in the prime of his career.
Nolan Arenado Colorado Rockies 3B
H2H ADP: Round 1 / Roto ADP: Round 1 / Age: 27
As much as any first-rounder, you know exactly what you're getting from Nolan Arenado, and it's decidedly first round-caliber. Given that all the other clear-cut first-rounders figure to be kept, you can't risk losing yours, especially when this one still has so many good years left.
Trea Turner Washington Nationals SS
H2H ADP: Round 2 / Roto ADP: Round 1 / Age: 25
It's looking less likely Trea Turner makes a big leap as a hitter, which means his peak may be that of late first-rounder, making him the first from this list who you could reasonably justify throwing back. But he's still the premier contributor of the scarcest category and a shortstop with most of his prime ahead of him.  
Bryce Harper Washington Nationals LF
H2H ADP: Round 1 / Roto ADP: Round 1 / Age: 26
Another 2015 still seems attainable for the outrageously talented Bryce Harper, but it's always something with him. He hit under .250 for the second time in three years, though it looked like bad luck this time. Still most of his prime left, too.
J.D. Martinez Boston Red Sox RF
H2H ADP: Round 2 / Roto ADP: Round 2 / Age: 31
Yes, J.D. Martinez is on the wrong side of 30, but now that he's primarily a DH and no longer subjected the wear and tear that used to sideline him for weeks at a time, he might have another five years of this sort of production.
Chris Sale Boston Red Sox SP
H2H ADP: Round 1 / Roto ADP: Round 2 / Age: 29
Chris Sale isn't always a first-rounder in redraft leagues, but in this format, you have to consider what's actually going to be available to you if you free up that pick. He's the most bankable pitcher this side of Max Scherzer and still on the right side of 30, so don't mess with a good thing.
Jacob deGrom New York Mets SP
H2H ADP: Round 3 / Roto ADP: Round 4 / Age: 30
You're obviously keeping Jacob deGrom after the year he just had, but it's a relatively mild discount for a player of relatively advanced age. The ceiling and the floor are both so high, though, and your chances at a true ace so rare. 
Trevor Story Colorado Rockies SS
H2H ADP: Round 11  / Roto ADP: Round 10  / Age: 26
Trevor Story broke out with first-round numbers last year thanks to a greatly improved strikeout rate and sudden proclivity on the base paths, but if he pulls a Giancarlo Stanton and starts swinging from his heels again, the outlook isn't so rosy. This discount is too favorable for you to play the pessimist, though.
Blake Snell Tampa Bay Rays SP
H2H ADP: Round 14  / Roto ADP: Round 13  / Age: 26
Blake Snell's below-average walk rate makes him less than fully bankable, and his durability hasn't been fully tested yet, which is a big deal to me in the age of diminishing innings. Keeping him is still an easy call, but now you know why he's 18th and not eighth on this list.
Walker Buehler Los Angeles Dodgers RP
H2H ADP: Undrafted / Roto ADP: Undrafted / Age: 24
Walker Buehler was the Dodgers' ace down the stretch last season, which is a massive achievement even with Clayton Kershaw showing signs of decline, but as with Snell, you can't just assume the workload will follow. With the way pitching usage is evolving, that's the big unknown for any up-and-coming hurler.
Christian Yelich Milwaukee Brewers LF
H2H ADP: Round 5 / Roto ADP: Round 4 / Age: 27
Sort of like the deGrom of hitters in that he was already good and suddenly became great, Christian Yelich is must-keep less for the modest discount and more because you don't want to get mixed up in a competition to get him back. It's true 2018 will likely end up being his best season, though.
Aaron Nola Philadelphia Phillies SP
H2H ADP: Round 6 / Roto ADP: Round 7 / Age: 25
Aaron Nola proved his durability en route to a third-place NL Cy Young finish last year, but of course the discount isn't as great for him as for Snell and Buehler. And I'll add that he may have had some BABIP and home run luck in 2018.  
Javier Baez Chicago Cubs 2B
H2H ADP: Round 16  / Roto ADP: Round 13  / Age: 26
Javier Baez's poor plate discipline means he pretty much has to have a high BABIP and home run-to-fly ball rate to be great, and while both are distinctly possible, it gives him a razor-thin margin for error that makes this discount less alluring than you might think for a near MVP winner. 
Aaron Judge New York Yankees RF
H2H ADP: Round 2 / Roto ADP: Round 2 / Age: 26
Speaking of thin margins for error, there may come a day when Aaron Judge no longer hits the ball with uncommon authority, making his poor contact skills much more of an issue than they are now. But after back-to-back years of it, I'm willing to view him as a perennial MVP candidate for the time being.  
Patrick Corbin Washington Nationals SP
H2H ADP: Round 14  / Roto ADP: Round 17  / Age: 29
The best swing-and-miss pitcher in the game last year did it despite a middling fastball and unorthodox pitch selection that made his slider his No. 1, putting him at risk of both injury and overexposure. But seeing as no one saw it coming, the price is far too good to pass up, even if his longevity is in question. 
Trevor Bauer Cleveland Indians SP
H2H ADP: Round 7 / Roto ADP: Round 11 / Age: 28
Trevor Bauer was probably the leading contender for AL Cy Young when he fractured his fibula in mid-August, and the underlying numbers back up the breakthrough. But the mostly mediocre track record combined with the fact he's nearing the end of his prime lowers his "longevity" rating.
Gerrit Cole Houston Astros SP
H2H ADP: Round 5 / Roto ADP: Round 7 / Age: 28
See Bauer, Trevor. Gerrit Cole feels like the safer bet given the Astros' aptitude for unearthing advantages from data, but they kind of put the squeeze on Cole workload-wise in the second half last year. Also, Cole is the costlier keeper of the two.
Eloy Jimenez Chicago White Sox RF
H2H ADP: Undrafted / Roto ADP: Undrafted / Age: 22
Eloy Jimenez is obviously overshadowed by Guerrero, as anyone would be, but he's a hitting prodigy in his own right.. Throw him back and you may be able to get him back at a decent enough discount for 2019, but if you had the foresight to scoop him up in the first place, why wouldn't you just keep him now?
Adalberto Mondesi Kansas City Royals 2B
H2H ADP: Undrafted / Roto ADP: Undrafted / Age: 23
The player who's shaping up to be the most controversial for 2019 could turn out to be way undervalued here as a standout base-stealer who also happens to hit for power and also happens to play shortstop. But there are questions aplenty about his bat and namely his ability to get on base.
Edwin Diaz New York Mets RP
H2H ADP: Round 11  / Roto ADP: Round 10  / Age: 25
Closers generally don't make for the best long-term investments, but Edwin Diaz was already thought to have tip-top potential, and he announced himself as king of the closers last year with a triple-digit fastball and unhittable slider. And he did it early enough in his career that there's no reason to think those skills will diminish anytime soon.
J.T. Realmuto Miami Marlins C
H2H ADP: Round 10  / Roto ADP: Round 11 / Age: 28
The new No. 1 catcher was considered more of an also-ran at the position a year ago, and even more could be in store for him if he escapes cavernous Marlins Park this offseason. But catchers tend to decline around age 30, which isn't so far away for him.
Gleyber Torres New York Yankees SS
H2H ADP: Round 23 / Roto ADP: Round 23 / Age: 22
Just from the perspective he was a top prospect who came through in his major-league debut, duh, you're keeping Gleyber Torres. But his path to greatness isn't as well defined as say, Ronald Acuna's, given that he's afflicted by similar contact issues but without the same power or speed ceiling.
Shohei Ohtani Los Angeles Angels SP
H2H ADP: Round 9 / Roto ADP: Round 10  / Age: 24
Considering Shohei Ohtani won't be available to pitch this year, being limited to DH duties for however much he's able to take the field at all, he may actually go later in redraft leagues than he did a year ago. But seeing as this is a keeper league and knowing full well now just how good he could be, you should trust that his present keeper cost will prove well worth it in the long run.
Victor Robles Washington Nationals CF
H2H ADP: Undrafted / Roto ADP: Round 28 / Age: 21
The surest contribution from Victor Robles (stolen bases) just so happens to be the scarcest in Rotisserie leagues these days, so by that measure, he's "safe." After an uneven season marred by a hyperextended elbow, though, I'm less than confident I know what he brings with the bat.
Freddie Freeman Atlanta Braves 1B
H2H ADP: Round 3 / Roto ADP: Round 2 / Age: 29
Freddie Freeman has become so bankable as a hitter, his line-drive swing and all-fields approach making him a steady source of batting average, that there's really no reason to throw him back unless you're just overrun with quality keepers. He has shown the capacity for first-round production in the past, too.
Jose Altuve Houston Astros 2B
H2H ADP: Round 1 / Roto ADP: Round 1 / Age: 28
The Jose Altuve of 2018 clearly isn't worth retaining with a first-round pick, but he has been a first-round fixture for so long and has such a unique profile that throwing him back seems short-sighted. He was plagued by a bad knee in 2018, so who knows? He could have another five years of MVP-level production in him.
Whit Merrifield Kansas City Royals LF
H2H ADP: Round 7 / Roto ADP: Round 6 / Age: 30
Whit Merrifield followed an out-of-nowhere, presumed-too-good-to-be-true 2017 with an even better 2018, becoming a more polished hitter with an even stronger inclination to run. The age isn't ideal, but he meets a desperate need while retaining his once-skeptical price tag.
Scooter Gennett Cincinnati Reds 2B
H2H ADP: Round 16 / Roto ADP: Round 14  / Age: 28
Scooter Gennett's breakthrough 2017 met with universal scoffs, but now he's widely regarded as one of the best at a weak position. True believers will reap the benefits twice over.
Ozzie Albies Atlanta Braves 2B
H2H ADP: Round 12  / Roto ADP: Round 9 / Age: 22
You'd think he'd be a slam dunk after he made the All-Star team as a 21-year-old, immediately showing the power potential most scouts only hoped he'd develop. But Ozzie Albies' numbers faded so drastically over the course of the season that it's fair to question how much of it was legit.
Eugenio Suarez Cincinnati Reds SS
H2H ADP: Round 19  / Roto ADP: Round 17  / Age: 27
A sluggish second half casts some doubt on Eugenio Suarez's breakthrough 2018, and at a loaded position, he wouldn't be missed as much. But value is value, and redraft are owners will be taking him at least 10 rounds earlier in 2019.
Jack Flaherty St. Louis Cardinals RP
H2H ADP:  Undrafted  / Roto ADP: Round 28 / Age: 23
Jack Flaherty didn't stick the landing in his rookie season quite like Buehler did, but he hung with him for most of the year and may also prove to have ace potential if he can cut down on his walks. Pitchers have a less predictable path now, though, with usage patterns changing across the league.
German Marquez Colorado Rockies SP
H2H ADP: Undrafted / Roto ADP: Undrafted  / Age: 24
With a 2.61 ERA, 1.00 WHIP and 12.0 strikeouts per nine innings, German Marquez was the breakout pitcher of the second half, catching the NL and entire Fantasy-playing world off guard with refined mechanics and more confident use of his secondary arsenal. Pitching half his games at Coors Field, though, he could get lost just as quickly as he was found. 
Mike Clevinger Cleveland Indians SP
H2H ADP: Round 14  / Roto ADP: Round 13 / Age: 28
After a second straight year of outperforming his peripherals, Mike Clevinger is more safe than scary, and obviously there's no downside to keeping him at this price. But seeing as he's at an age when it's no longer reasonable to predict growth, he's probably more of a mid-rotation arm than a front-liner over the long haul.
Mitch Haniger Seattle Mariners CF
H2H ADP: Round 24 / Roto ADP: Round 19  / Age: 28
If I could guarantee a similar run and RBI total for Mitch Haniger in 2019, I'd have him higher on this list, but with the Mariners dismantling the lineup around him, it's pretty much a lost cause. He's a value at last year's price tag, no doubt, but chances are he won't be a true standout this season.
Jameson Taillon Pittsburgh Pirates SP
H2H ADP: Round 17  / Roto ADP: Round 17  / Age: 27
Drafted second overall way back in 2010, Jameson Taillon's growth has been glacial, and even now, his bat-missing skills lag behind everything else. But there are no obvious red flags after a breakthrough season that saw him handle an ace workload down the stretch.
Blake Treinen Oakland Athletics RP
H2H ADP: Round 14  / Roto ADP: Round 14  / Age: 30
In a role as volatile as closer, which has produced innumerable one-hit wonders in Fantasy, a 30-year-old breakthrough who previously wasn't even regarded as a bat-misser would seem like a so-so keeper. But Blake Treinen's numbers were positively other-worldly and the justification for them seemingly airtight.
Max Muncy Los Angeles Dodgers 1B
H2H ADP: Undrafted / Roto ADP: Undrafted / Age: 28
I wish the Dodgers had as much faith in him as I do, but even acknowledging the totally unjustified platoon concerns (look at the splits!), Max Muncy's rise from A's outcast to Jim Thome doppelganger is the sort of thing you pray for in this kind of keeper league.
Xander Bogaerts Boston Red Sox SS
H2H ADP: Round 6 / Roto ADP: Round 7 / Age: 26
In what was his most believable performance to date, Xander Bogaerts proved to be a competent enough all-around hitter for owners to commit to him as their long-term shortstop. Will he return much more than sixth-round value? Probably not, but it's nice to know a premium position is already filled by a player whose prime is still ahead of him.
Matt Carpenter St. Louis Cardinals 2B
H2H ADP: Round 10  / Roto ADP: Round 12  / Age: 33
After a couple injury-marred seasons dragged down his value, Matt Carpenter came roaring back with early-round production in 2018, rewarding his most faithful with a nice discount for 2019. But it could still backfire, given his age and health history, and it's not like he's a building block of any sort.
Matt Chapman Oakland Athletics 3B
H2H ADP: Undrafted / Roto ADP: Round 26 / Age: 25
Matt Chapman certainly proved to be a capable starter in Fantasy last year and will go much earlier in drafts this year as a result. But is his bat impactful enough to devote a precious keeper spot to it? Eh, it depends how many you have.
Miguel Andujar New York Yankees 3B
H2H ADP: Undrafted / Roto ADP: Undrafted / Age: 24 
What we saw at the plate from Miguel Andujar in 2018 may prove to be exactly what he is, but hitters with high batting averages and low on-base percentages are never as valuable in real life as in Fantasy. And he's such a liability defensively that the Yankees' commitment could quickly wane.
Jesus Aguilar Milwaukee Brewers 1B
H2H ADP: Undrafted / Roto ADP:  Undrafted  / Age: 28
Pegged as a platoon bat with an unforgiving defensive profile, Jesus Aguilar's rise to Fantasy prominence was one of the most unlikely developments of 2018 ... which is why you have to figure he'll have as short of a leash as his predecessor. His batted-ball profile certainly supports the production, though.