The Wii without question. It has gotten numerous Sonic games that have sold well including Sonic and the Secret Rings which has sold well over a million. And he has been a big part of two mega selling games, Mario and Sonic at the Olympics, Super Smash Brothers Brawl. The latter was sure to be a hit regardless but I'm sure a big reason for the success was the novelty of Mario vs. Sonic for the first time in a video game.
I'll come up with something better eventually...







