My only complaint about the GC controller is the Z button. It should have been placed underneath the controller somehow, like the trigger of a gun, because that's the way the Z button is traditionally used. Putting it up on the shoulder made it more awkward and frustrating to use.
I do think the rest of the GC controller was genius, though. Having the buttons shaped, sized, and colored differently made them much easier to use when you're in the middle of a game. There was much less need for hunting and pecking, and it was very unlikely you would hit the wrong button by mistake.
In controller terms, I would say the GC was the best, then the XBOX and then finally the uninnovative PS2 .