I only own the PS3, and of course I think it's the best out of the three, otherwise I wouldn't have bought it... However, I really think that in this gen, you really can't put one console over the other, since they all serve a different profile of gamers in my opinion... Wii: innovating controls, best offline multiplayer, NINTENDO , easy and fun / PS3: great "multimedia station", technically most advanced, great exclusives BESIDE all those generic FPS (ok, that was subjective), free online service, but probably the best choice for single player gamers / X360: very good value, best online multiplayer, also great exclusives, especially if you are into shooters....
It's really a matter of taste in this gen I think... as said before, I only own the PS3, but also got sympathy for the other two... but I'd probably rather get a Wii if I bought another console, since I actually really like Nintendo's approach... if the 3rd party support will get better, that will be a hard test for my bank account
Not so much into the Xbox 360, because I don't like FPS (put aside Half-Life/NOLF and a few others) and haven't got much interest in online gaming... also, I owned the original X-Box, which rather disappointed me... but maybe that's just because I owned a Dreamcast before