Of the three, purely as a games machine, I think the GC shades it. However, hurrah, hurrah, there's a bit of a surge in retro gaming. Not just Mega Drives/SNES/Amiga/Commodre/Spectrum etc. but machines and games for the likes of Dreamcast and Saturn are now appearing in some 'retro' stores. I bought a Dreamcast recently for £22. Most of the games can be picked up dirt cheap and there are some cracking games on it.
The Saturn struggled. It didn't have the capabilities of the PSX when they hit the shelves in the mid 90s but the one cracker of a game that appeared on the Saturn was Athlete Kings. Of it's type (button bashing arcade athletic sports), I have yet to see a better game.