TruckOSaurus on 27 January 2014
It'll be close. Some data:
The PS360 sold 3.3 mil.
The current highest selling 3rd party game on Wii U is Lego City with 690k.
I'm going to side with the Wii U 3rd party being the highest seller mainly because I believe there's not that many people wanting to repurchase Tomb Raider and that for those who haven't played it yet it's available for dirt cheap on Steam.
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