The wired controller is better of course. If cable length is a problem, get a GC cable extension cord.
I recently bought a used GC controller for just 15 € (in great condition), didn't need an extension though. You should be able to find one for a good price, but look as soon as possible because they'll get scarcer soon, with SSBB launching and all that.
My Mario Kart Wii friend code: 2707-1866-0957