I think it will be Animal Crossing. If it was just the game, it would still sell extremely well, probably 7 or 8 million. A lot of people will also be interested in WiiSpeak and that will be the extra incentive to get the game.
One aspect of this game over the GC version that I don't think anyone has mentioned is that the Wii is online where the GC was not. So that alone can make Animal Crossing a better experience. I'm sure that playing the DS version online helped pushed sales. So I think Animal Crossing can cross 10 million and who knows? I wouldn't be shocked at all if it does 15 million or more since the Wii will end up selling at least 80 million in it's lifetime if not over 100 million.
I'll come up with something better eventually...
