Gamecube controller is best for me because muscle memory. I really don't like using the 3DS smash, the circle pad is just a pain in the arse and the screen is too small for me as I have an original 3DS.
I... I have a confession to make. I use theclaskkintrul...
I said I use the clasikintrulr.
...Oh fine, I use the Classic Controller. Not the Pro, the one that's pretty much a SNES controller with some analog sticks. I like my buttons the same size and my grab & shield buttons next to each other.