I work for a pretty well known company that sells games, and i own both the xbox 360 and ps3.
From my experience, the 360 is just better value for money.
You get a better selection of games, the console is cheaper, at times the games are cheaper than the ps3 conterpart, there are plenty of cross platform games that perform better on the 360 because its an easier system to write a game for.
The ps3 is the way to go if you want a blu-ray player, or to use it like a media center, but if you after just gaming, especially if its online, the 360 is the way to go. There is hardly even a title on ps3 that actually even has 1080p playback even though the games are on blu ray lol (costs too much to do apparently).
Im not saying the ps3 is bad, the 360 is just better for games, and it has Left 4 Dead
But yeah thats just my opinion.