I don't know who "should" win it, but the RB1 will be a competition that will come down to likely 3 players. Would like to see A.Williams bring the heat in camp and preseason and get himself in the mix of it. But likely be Motor, Moss, or Breida.
With that said I don't think there will be much difference between rb1 and rb2, anyways because they will likely be rotating much of the time imo. Anyways, hopefully see all RBs make a difference.