It's hard to say. My top though, not in any order are:

Derrick Williams - He's already built as an incoming player, he's quick, can shoot, all of that. I think it depends where they play him, but he's incredibly talented for a big man. I think he'll be a monster three on the offensive side, but on D, I don't think for his rookie year he'll be able to guard the Lebron's, Melo's, and KD's. He has the athleticism though to be a presence though.

Kyrie Irving - I didn't see him play enough to really rate him. But, if he's the 1st pick after missing most of his Freshman year than he must have potential that teams are interested in. And, he's a PG, and lately they have been running the league.

Jimmer Fredette - He's a hard worker, with unlimited range. I think he's pretty strong and crafty. He'll just need to get faster defensively for guards like Westbrook and Rose.

Kemba Walker - Proven winner. Quick, can score the ball effortlessly, and his defense and jumper is coming along. His downside is his height, but he'll get better at it. It'll take time though but he's a competitor and has one of the better work ethics, if not the best out of this whole rookie class. I think he's a definite canidate for ROY.

DERRICK WILLIAMS!!!!!!!!!!!

JIMMER