I own an Xbox 360 and the Wii, and I've owned a PS3. I think PS3 is best if you're not a serious gamer because no one really talks smack on there. Xbox is better if you're a more intense competitive player, as it has Halo, Gears of War, and plenty of trash talk. Wii is the most laid back, and is very good for single player and co-op games. It all really depends on what type of gamer you are, and how often you play.
I own them all but I like the PS3 the best out of them all. I don't really feel like paying to get online when I can have it for free on the PS3. Plus I like the feel of the controller for the PS3 the best.