I got the adaptoid and I can't understand why anyone would want a gamecube controller to use for N64 emu.
First of all, with the adaptoid/n64 controller youre literally as close to the real thing as you can get.
Next, with the Gamecube controller you have no way to lay out buttons for A, B, C1, C2, C3, and C4 unless you do all C buttons as analog as they are on the GC.
Finally, the N64 controller is perfectly backward compatible for all other previous console emulation .. in other words, NES, Master System, Genesis, SNES, and etc. all work fine with the N64 controller setup. All the buttons are there and in the right place (except for "Select" which works ok with the Ztrigger and is rarely used anyway)
On the other hand, the Gamecube puts priority on analog directional input, so it has a tiny GBA sized D-pad. And, they finally figured out that probably 80% of the time only one button is getting pushed, so they made one huge action button, one secondary, and then put x&y along the perimeter as auxiliary functions. This works great with GC games that are developed FOR the GC, but could really suck on N64 games. It could be done, but why bother when there's a effective way to do it already with a real N64 controller?
Now, with all that said, this is important too: IMHO of course, but even though I prefer using the adaptoid/n64 controller for emu, the Gamecube controller is the BEST controller, console or PC, I've ever used. Hands down. Without a doubt.