I've had an Xbox 360 for about a year now, and it's already stopped working. So PS3 definitely has better build quality.. You can't even touch your 360 while a disc is inside or you're set back another 50-60 bucks >_>. That's happened twice to me so far.
But as for the games, It's really just preference. PS3 also has free online, which Xbox lacks. One thing I like more about the 360 though is the controller. It's usb so you can use it for your PC too, which is a bonus. I don't like the PS3 controller much. The only real reason I have a 360 instead of a PS3 though is that at the time of purchase, I didn't know a single person in my province that had a PS3..
If I had my time back I may have just bought one anyways.