What xbox 360 game to get?

ok i have enough money to buy one game... i have bioshock, halo 3, gears of war, saints row, asb 2007, gun, perfect dark, burnout revenge, etc. etc. so i was wonderin what a good choice would be to add to my collection... as u see i am a big fan of shooters and sports... i was thinking of either m effect, call of duty 4, kane and lynch, or ins creed but if you have another selection i am open to ideas