XBOX 360 if you want to not have to pay for your games (it's a hassle getting to know how to mod and everything though, after that you're set)
PS3 if you don't wanna bother with modding. I have both, I use my PS3 more and I play COD: MW3, it's fun and you'll like it the most out of all the games.
New game mode, Infected = amazing