Oh god, I hate that SuperPad Plus controller with a passion. Kind of an awkward shape and the c-buttons are in the wrong place. That and it's a Sega to hack.
Anyway, my favorite controller would probably be the 360 controller. Only used it a few times, but it's BASICALLY an XBOX S with wireless and shoulder buttons instead of the black/white ones. The S rocks, and by extention the 360 controller is better.
Most comfortable controller I'd say would be the Dreamcast one. It's awkward at first but after a little playing it feels natural. However, the controller itself is somewhat lacking. Only one analog stick (nice stick, bad cap), crappy (but usable for anything that's not a fightyer) d-pad, and awkwardly placed start button. I do like the VMU system with the window, and that they at least tried to fix the "cord out the bottom" with that little clip, which works well but leaves dents in the cable. Overall a good controller, but not a great one.
SNES controller is the best retro one. It felt good for the controllers of the day, but is still kind of awkward compared to modern controllers with handles. Good button layout, about the highest evolution of stickless controllers. Genesis controllers=sucks. The 3-button is lacking in buttons and is too big to hold like a SNES controller and too thin to hold like a modern one. The 6-button is just plain too small for the amount of buttons, but the layout is great for fighters.
I will also praise the N64 controller for being strange, yet working surprisingly well. It seems to me like Nintendo was too cheap for two analog sticks. They didn't want it on the same side as the d-pad, as that would make shooters impossible to play, so they put it in a separate prong in the middle. C-buttons are kinda odd, but work fairly well as just normal face buttons. Someone mentioned that the controller was pretty much made for SM64. I doubt that; if so, why would it have the d-pad and (almost never used) L button.