Right now I am saying GameCube because it had tons of great games that everyone looks back at and loves yet they were ignored in the midst of everything else. Also I'd pick N64 but it sold about 11m more (22mGC 33mN64). Wii U could replace GameCube though, depending on it's sales and games at the end of this gen
XBOX ONE/Wii U/3DS/PC
RIP Iwata 12/6/1959-7/11/2015
Thanks for all the great memories!