I have a 'cube, and I'm pretty pleased with it. Everyone above is right - PLII for audio, component pro-scan (480p) for video (provided, of course, the game itself supports pro-scan - most do, a few don't).
All three systems have great games. But if you play infrequently and are largely interested in a nostalgic experience with the kinds of games you recall from the SNES days, I think a Gamecube is a good choice. Mario, Zelda, Metroid, et al. Plus it gets the sports games from EA, etc.
I maybe game 5-10 hours a week these days, and as a result, this is the system that gets the most use out of me as a result. I think if you were really going to put in some serious time - with role playing games and/or long online gaming campaigns, I would suggest looking at the PS2 or Xbox.
I have all three. But given my time constraints, I tend to play games that I can just pick up and play for a while. I've just found that the 'cube meets MY PERSONAL preferences on that score the best.
As always, your milage may vary.
