When I think Fighter of the Year, a couple names come to mind...
Brock Lesnar (of course) - The guy debuted in Febuary. He lost his first fight, had another in August, won, and then another fight in November winning against Randy Couture. The guy's UFC record is 2-1. In his first year fighting he won the World Heavyweight Championship. What more can possibly scream FIGHTER OF THE YEAR?
Forrest Griffin - You have to give Forrest credit. He was the first Ultimate Fighter and proved to everyone that winners of the Ultimate Fighter can eventually become champion. Plus he beat Rampage Jackson which is a pretty big accomplishment in itself.
Anderson Silva - Silva still undefeated in the UFC. He is the current reigning UFC Middleweight Champion, plus on top of it all he moved up to Light Heavyweight and destroyed James Irvin.
I don't think I would be able to decide, but just off the top of my head the order is as follows...
1. Lesnar
2. Silva
3. Griffin