You can get usb snes controllers,but you can also get an adapter which lets you plug an actual snes controller into a usb port
Here's what I used until I dropped it too many times and it broke. http://retro-bit.com/retrolink/controllers/snesr-style-usbr-wired-controller-for-pc-macr.html
If I'm playing on emulator (which I don't use for SMW any longer, but do use for ALTTP,) I've got a few SNES controllers that I've converted for USB.
I can recommend the usb controller from ibuffallo. I use it for SMB1, SMB3 and SMW. I've tried a lot of USB controllers and the D-pad and the buttons was by far the best.
I got a wii classic controller and the controller is really good, especially the D-Pad is nice, but i didn“t found any good adapter for usb to use is on pc. All 3 adapters i have do stupid things like "ghost inputs".
I would buy another one and cut the wire off then put a USB port and connect the correct lines to it and use electrical tape to tape it up and it worked for me
I've tried playing on keyboard but I can't play well at all. It's awkward and foreign to me. Being a person who has been a console gamer since around 1988, I can't get the hang of playing on a keyboard. I imagine it's a lot easier if that's what you start off with.
I use just a ps3 controller i was weird when I started but now it feels normal