With PC sales, L4D will easily win.
Without PC sales, it will probably be R2, due to many factors:
- R2 will probably get a bundle at some point.
- R2 is the sequel to a well know PS3 game.
- L4D is primarily an online co-op game that requires an internet connection and an XBox Live Gold membership to play online, limiting it's audience on the 360. (edit)








