If you're only considering consoles, and considering backwards compatibility, the 80GB PS3 is the clear winner, as you can play the entire PS2 library (the games you cannot play are *really* rare these days, as Sony continues to improve its BC), plus PS3 games.
I'd put the Wii in the #2 spot for a similar reason: the GC had a lot of great games, which you can find cheap, and frankly, they aren't much different from current-gen Wii titles.
The 360 has the best "current-gen" lineup, but its BC selection would be medicore even if the entire XBox library was supported, which is isn't... not even close. Overall I'd have to put it in a near 3rd, right behind the Wii.
Nothing even comes close to the BC PS3s, if you consider their vast PS2 library diversity.







