Thats a good question. Well lets see, Melee sold 6.58m WW and Mario Kart Sold 6.60m WW. Thats pretty much a tie. Melee sold more than MK in japan and America but MK sold more than SSBM in Others. Since most of the Wiis are in the US I'm gonna say Brawl will win acording to VGchartz cause Brawl will most likely sell most there. It will be close but in the end, Brawl will win.
Official member of the Sonic Support Squad! 
Bet with OriGin: Within 1 year Super Smash Bros. Brawl will be ahead of Mario Kart Wii (when aligning the one whole year from each region). 2 week ban from Vgchartz for the loser. Edit: Darn! Looks like OriGin will win. 







