There is no definitive "best."
Everybody is different, so everybody enjoys different game styles. Graphics freaks would go for the PS3, people who are Halo fanboys would go for the 360 just for the title, and people who want to follow Nintendo's franchises, game on a budget, or [parents of] children go for the Wii. Not to mention people who like party games.
Personally I like the Wii, but I'm a sucker for the Virtual Console. Also, I believe if a good FPS comes out for the Wii then that'll just knock that console out of the park.