I'd say Wii, 360, PS3 in that order.
The Wii seems like the one most geared toward the casual gamer, or a gamer who just doesn't want to shell out lots and lots of money. No fee to play online (Though the online gaming hasn't been fully realized yet on the system), games that aren't hitting 60 bucks apiece yet, and downloads dating back to the NES. Not only is the control scheme a novel idea, but it's far easier to use than it would seem at first glance. Only drawbacks would be the battery life of the controller, the lack of warning on said batteries before they die, and the current shortage of great games.
360 may not have a LOT of great games, but the few FPS's and other games available that are good are REALLY good. Add in the downloadable materials, the user scores, and other unique aspects, you have a well rounded system. Drawbacks would include, again, the lack of great games, the prices, and that's pretty much it.
PS3... has potential, but that's not saying much now. The Wii has various Nintendo-specific titles, 360 has Gears of War and Halo, PS3... is losing its unique titles. Devil May Cry 4 is coming out for the 360, and I believe Final Fantasy XIII is as well. The insane prices for a system so advanced that some TVs can't keep up with it ensures that your average gamer isn't going to go near it until it drops at least two or three hundred dollars in price. Higher priced games than the Wii, system problems, and a distinct lack of ANY good games leave it in a rut for the time being. Time will tell if the PS3 will thrive in the long run, but for now it's definitely taking last place in my eyes.
All in all, all three consoles have a LOT of potential. When you go back and play an NES game, or even an SNES game, it's astounding to see just how far video games have come. And hopefully, there's still room for improvement.