well assuming every other console went kaputz, all the games would be stuffed onto whatever's left. so my vote goes to the most versatile of them, the PC. then we COULD still see all the same stuff, just in different forms.
among the actual consoles? I dunno. the Wii is crap, but mostly because it has competition with better hardware. if the others were wiped out I'd prefer to play games made to be fun rather than made to look good. however, nintendo's been rather iffy lately so I don't know if I trust them to keep it going.
the PS3 would also probably be good if the others were gone, but I think I'd prefer the 360 of the two, just because they offer better services (even if you DO have to pay for them) and I can be sure that M$ would do whatever it takes to do the best job and make the most money possible (while cutting every corner possible, of course, but hey, it's M$).
anyway, that's my opinion and my reasoning. feel free to flame all you like.