When you say "best", I'm thinking of the 1 player on the field that makes the difference between a win and a loss every week. 4-5 people come to mind; Michael Floyd, Kyle Rudolph, Dayne Crist, Armando Allen (and Brian Smith as the defensive game changer to be most improved).
If I had to pick one, I might actually go out on a limb and pick Kyle Rudolph. He's a safe bet in Brian Kelly's offense to be extremely productive. With the QB situation a little shaky, I think Kyle shows the most glaring production. However, I see all the players I mentioned, having a much improved or great season in 2010.