You should buy 2 wavebirds (Nintendo made wireless controllers for GCN). I had numerous b button sticking problems and c stick (yellow stick) messing up on wired controllers. I then found the wavebird and they have never messed up for c-stick and b button sticking (only problem is after constant wear some of the l r triggers make metal sound when hitting down on them, but they don't stick or interfere in any other way). Wavebird controllers are the most sturdy GCN controllers you can find plus they are wireless. Only drawback is they don't have rumble to preserve battery life but that never bothered me.
GCN Controller (Wavebird) > Classic Controller for Smash. You should just buy 4 Wavebirds in my opinion (I have 4 Wavebirds)







