For the Wii, I think it boils down to how much you like Nintendo games. That's why I have one. There are also some nice compilations from prior generations and enhanced ports available.
For the Xbox 360...honestly, I liked its predecessor more, even if that also had too much overlap with a Windows PC. Then again, the Xbox Live Arcade has some compelling ports and remakes of existing titles (Radiant Silvergun released outside of Japan, in HD to boot? HELL, IT'S ABOUT TIME!), and maybe Kinect will turn out to be something really good for all I know.
The PS3 has more compelling exclusives than the X360 that don't involve XBLA (whose interesting titles are, as I said, ports/remakes), and you don't have to pay for online multiplayer. However, they've really neutered the console from the original CECHA revision, taking out PS2 backwards compatibility, support for certain media formats, and who knows what else to get the costs down. Oh, and the whole Other OS debacle and Sony blatantly lying about not planning to remove it at all.
Also, I'm surprised to see a certain someone in here who has very literally said "I don't game, or give two ****s about gaming."