I know i'm one of the few that doesn't think trading down is the best idea, but if we do, the player i'd like selected is Ryan Nassib. In my opinion, the best QB in the draft, and by FAR the one with the most potential. He played behind a leaky line with awful receivers and not a very good running game, yet got better as the season went on. His accuracy in short and medium passes is A+ and has the arm strength to make deep throws. What i like most about him though is his pocket awareness and decision making. He's got a exceptional feel for everything going around him, and does a excellent job climbing the pocket. He could easily start, but i think sitting him for a season would be beneficial and he'd only be better for it. Honestly, if Buffalo doesn't take him at #8 and we traded down to the late teens, early 20's i'd take Nassib in a heartbeat. Potential wise, he's probably top 5 in the draft.
Here's a nice look at him from Russ Lande, a pretty good evaluator. Ryan McCrystal and Greg Cosell also have him as their #1 rated QB.