S.Peelman on 03 June 2017
Going by number of third party games I actually bought (or got); N64 > GC > Wii > WiiU.
Though that's probably not really fair since I just have way more N64 games than I do WiiU games, about 50 for the former and like only 12 or something on WiiU. 
Gamecube could probably have been much higher had I actually payed attention that gen.
