The problem with the GameCube is that it gets left out in the cold. When publishers release a "multi-format" game, it's always on PS2 and Xbox, hardly ever on GC. It was the same with the N64, but at least then there was the reason that a conversion would mean using cartridges instead of CDs. Not so with the GC, as its discs can hold as much data as its rivals'. Publishers just seem to have written off Nintendo, meaning that most of the decent games on the system have to be developed in-house, and those aren't enough to attract the majority of gamers.
I've had a PS2 for almost a year now. It felt like selling my soul to the Devil when I bought it, because I still have irrational feelings of sentimentality towards the games industry, and sorely long for Nintendo (in the absence of my first favorite, Sega) to rise from the shadows and put the faceless corporate bullyboys in their place. But in the end, of course, it had to come down to the games, and the games I most wanted just weren't available on the unloved GameCube.
I can't comment on the Xbox as I've never played it, but if I ever need an expensive plastic breeze block for whatever purpose, I'll be sure to order Microsoft's console.