If everyone hits their potential I'd go with Gholston personally. I think both Longs are already pretty close to their potential--you know you're getting an excellent football player. The one's with loads of unrealized potential but the highest ceilings are guys like Gholston, Groves, Otah, Williams, etc. The only thing preventing them from being all-world is that they're just not the best football players at present, they're getting by on insane athletic ability. But if they become great players, students of the game, technicians, and acquire the instinctiveness of players like Zach Thomas, then those guys have HoF potential. The problem with the Longs isn't any of that, it's that their ceilings are much lower than some of the other guys ... the reason they're going to be at the top of everyone's draft boards is because they're already dominant football players ... not because of their potential to improve. Someone like Groves though has the potential to be truly great ... but it's going to take a lot of improvement as a player for him to get there in the NFL.
As for QB's, I don't think Ryan has the potential to be a franchise QB. Brohm, Henne, Flacco, I'd say one of them might eventually become top QB's. Brohm is the best of the bunch I think, and he's going to be ready pretty soon. Flacco and Henne are sorta projects IMHO, and they'll both need 3 years in the NFL before they really start to shine.