The 360 has a much wider, more complete library while the PS3 allows for more technical tweaks of the system and offers an edge on power. The Wii failed me. The only appealing part of the Wii in my opinion was the Virtual Arcade and let's face it, we can just use ROMs for that.
I prefer the XBOX 360 myself, and it's not because I'm a diehard XBOX fanboy.
I actually play on both consoles; I own a 360 and I play on my neighbours PS3 fairly regularly. I've owned both the PlayStation original and a PS2, as well as the original XBOX, and quite frankly I've always thought the XBOX outshined the PlayStation. Not that I don't like the PlayStation - far from it.
See, I actually have a lot of respect for the PS3. I think it's a great console. I just prefer a lot of things about the XBOX 360. It seems to have a better gaming interface, it's more accessible for me. It has so many great exclusive games, many more than the PlayStation. The controls seem more...suited. The graphics may not be entirely up to the PS3's standards, but they are still excellent. The performance is great, the power is just right, there's almost nothing I dislike about the 360, except that you have to pay for Live, and Microsoft Points for add-ons.
Now, as for the Wii...I'm not really a fan. I don't consider it to be a console, really. Don't get me wrong. It's good for a fun time. It's definitely a great family platform. I just don't think it matches even the GameCube in that I haven't seen anywhere near the same playability with those controls. I could be wrong, but from my experience, it just doesn't work. Not to mention they should have worked a lot more on the graphics.
So for me, the XBOX 360 takes first place, followed closely (but not too closely ) by the PS3.
That's why you go get a Gamecube controller and use it on the Wii
I've got to go with the Playstation 3. Since I'm not into games like Halo and Gears of War, the 360 has never really been my first choice and the fact that you have to pay for Live is another. My big problem with the 360 is that almost everyone I know has gotten the Red Ring of Death and when they send it in, it's taken a month to three months for them to get it back and that's just something I wasn't going to risk.
I had a Wii but sold it to get the PS3 for Christmas. I liked it because it was more interactive then other consoles because you actually had to move around for a bunch of games.