PS3 is dead in the water. Development is slow, games are too hard to code, and they still can't figure out what they're doing in terms of online services. Buy it if you need a cheap Blu-ray DVD player.
It's pretty much between the 360 and the Wii, and Microsoft even said they'd prefer if you bought both (basically to kick Sony out of the picture then do something nasty with Nintendo) but yeah, the 360 is already in its prime, and there's so many good games out for it. The Wii is just plain fun and innovative.
Take your pick, but my vote goes for the 360. I've had mine since launch, and there's been no problems and I couldn't be happier with it.