If you want to know who Penn State's starting quarterback will be this season, you either need to be a close, personal friend of Bill O'Brien, or you just need to wait until Saturday when Penn State opens the season against Syracuse.
O'Brien has played his cards close to his vest throughout camp this summer, so it's hard to know exactly which way he's leaning, if he's even leaning in any direction. It's possible he just doesn't know yet, though O'Brien's background working in the NFL and with Bill Belichick causes me to believe he knows exactly who his quarterback will be and he just doesn't want to let anybody else know.
Neither quarterback has ever played for Penn State. Ferguson is a junior college transfer and Hackenberg was a five-star quarterback in Penn State's 2013 recruiting class.
If I had to make a guess -- and this is with absolutely no inside info, just to be clear -- I'd say Hackenberg will be the guy. Penn State isn't eligible for conference titles or bowl games for a few more years, so I just think O'Brien will want to get the freshman on the field now to prepare the program for the future when it will be eligible again.