Based on my experience:
Wii: Super Mario Galaxy. Runner up: Metroid Prime 3
DS: Legend of Zelda: Phantom Hourglass. Runner up: I <3 Pheonix Wright, but Diamond and Pearl have it bet.
Others, based on whatever.
360: Bioshock. Runner up: Halo 3
PS3: Probably Call of Duty 4.
Wii: Super Mario Galaxy. Runner up: Metroid Prime 3
DS: Legend of Zelda: Phantom Hourglass. Runner up: I <3 Pheonix Wright, but Diamond and Pearl have it bet.
Others, based on whatever.
360: Bioshock. Runner up: Halo 3
PS3: Probably Call of Duty 4.