The wii has plenty of fighting games (more than the 360 and PS3 if you include vc ):
Dragon Ball Z budokai tenkaichi 2-3
Bleach Shattered Blade
Naruto Clash of Revolution 1-2
Naruto Shippuuden: Gekitou Ninja Taisen EX-EX2
Guilty Gear XX Accent Core
King of Fighters Orochi saga
Super Smash bros. Brawl
Castlvania Judgment
Mortal Kombat Armageddon
Tatsunoko vs. Capcom (import only)
and for vc:
Street Fighter 2’s from SNES and Sega Generation
Art of Fighting 1-2
World Heroes
Fatal Fury 1-2
Virtual Fighter 2
Samurai Shodown 1-2
King of Monsters
Eternal Champions
And there still unreleased titles:
Samurai Shodown Anthology(Mar 09)
TMNT fighter (TBA)
Toshinden (TBA)
The real question is what kind of fighting games do you like. The wii is more of a classic/retro 2D and nontraditional/free-roaming 3D fighter console. While the 360 and PS3 are more traditional in both 2D and 3D aspect. I tell you this if you already have a PS3 you’re not going to find much if any fighting games for the 360 that can not already be purchased for your PS3.