Which should i buy need for speed shift or forza motorsport 3 and what are the pros and cons of both games?

Neither, get Assassins Creed 2.Which should i buy need for speed shift or forza motorsport 3 and what are the pros and cons of both games?
Well both of them are awesome next-gen racing games, both have awesome graphics and are just awesome it's up to you which one you like all though I'm seeing alot of ppl go for Forza 3 only big difirence is: NFS is for PS3 and XBOX360 and Forza is exclusive to XBOX360