What do you think? If we don't include bundles like WiiSports and WiiFit.
I'd have to say it will either be SSBB or Mario Kart Wii. SSBM and Mario Kart:DD were the best selling games for the cube, and they will be among the best sellers if not the best sellers themselfs.
(But maybe a new zelda game could go for the spot of best seller?)
What do you think?