Gamecube end of June 2003-9.63m
Wii U end of June 2014-6.68m
Gamecube is still ahead by about 3 million. I will give Wii U some slack tho considering its still twice the price of Gamecube at this point in its life so maybe future price cuts and Amiibo success can help it get over Gamecube lifetime sales but its not currently looking good.
When the herd loses its way, the shepard must kill the bull that leads them astray.