It's either Yi or Horford for me, I'm really leaning towards Horford though, especially if the Hawks manage to make the playoffs.
Durant hasn't really impressed me. He has a license to chuck and is a complete liability on defense...
Sean Williams would be my dark horse, but realisticaly speaking I can't see him beating out Yi, Horford, or Durant. He'd have to have a pretty crazy run of games in order to do that...