Cube controller hands down. I've tried every other option and none of them are comparable.

The wiimote+nunchuck combo is ok, but by now my brain is hardwired to use the cube controller to such an extent that it takes too much thought to figure out which button to press with which hand to be quick enough in a match. If somebody had never played Smash before, and they just started with the wiimote+nunchuck I think they would do alright.

But the cube controller is absolutely perfect for it. Nothing else even feels close to me.

wiimote + nunchuck, though I dont use the motion controls and never will!!!

gamecube controler is the way to go!!!

I don't have Classic and I used to play Melee from time to time. So yea, gamecube controller.

Here it goes:
GameCube
Classic
Wii + Nunchuck
Wiimote.

GO OLD SCHOOL!!!!

New School

gamecube controller.

Wii remote, though I like each of the settings. Sometimes I find the nun-chuck and motion controls fun and entertaining, but if I want to win it's all about the Wii remote.

8-bit style rules!

Gamecube. You are doing it wrong with anything else.  I don't own a Classic Controller so I don't know about that.

I used the GC controller only. Wii mote alone felt weird, and Wii mote and Nunchuk was serviceable, but not as good as GC alone.

I used WiiMote/Nunchuk. Worked just as well as the GC in my opinion. Only you dont have the hassle of plugging it in and out after play.