I own a Playstation 3 and a Xbox 360.
By far i prefer the PS3 because I prefer its exclusive titles such as Uncharted, Gran turismo 5, Metal gear solid 4, Wipeout, Ratchet or Motorstorm...and what's upcoming is a musy-have for me : God of war, next Ico's, Tekken, Final fantasy 13 versus...
anyways a lot of games are multiplatform, but I still prefer buying these on PS3, because when it's online, I don't want to pay to play online.
Xbox 360 is still good for games such as Mass effect (the DRMs being terrible on PC) or Dead rising.
I'm never buying a Wii however, I think it's too expensive for what it is, I hate the fact they dont put any efforts into graphics, and I feel that anyways, the gameplay is too simplified by the wiimote...it's hard to get any depth playing this way.
PC still wins them all though 