I would have to choose the ps3. Even though I already own one. The X360 is really nice, has Halo 3 and a few other exclusives. But to be honest, my friend has a 360, and if I want to play it I can just mooch off him for a bit. The PS3 on the other hand, has a lot of potential and extras, namely Blu-Ray, DVD is dead. Built in wireless, upgradable hard drives, downloadable demos, games, Super Stardust HD rocks..
I don't think the PS3 is that far behind. The 360 has been out for over a year already, and the Wii just appeals to the mainstream crowd.. lower price point and pick up and play games. The PS3 is the most expensive out of all of them, but honestly the people who do think that it is really that expensive just doesn't value the Blu-Ray capabilities, which is fine, its their choice.
I had the Wii at one point, hell, I even camped out to get one on lauch date. But after a few weeks, it just started collecting dust. I might pick one up at a later date, but I'm not sure. It just felt like I was playing last generation games in a new control scheme. And now, there are like... 8 different peripherals coming out for it, steering wheel, balance board, light gun. I don't thing I have enough space for all of that, lol.