Didn't really want to open this can of worms, but both tags are currently being used so...
Japanese title = garou or garou_densetsu = 69 tagged posts
English title = fatal_fury = 183 tagged posts
Casting my vote for Garou Densetsu even though Fatal Fury will be more recognizable to people who visit this site. I wouldn't mind so much if Fatal Fury was a literal translation of the Japanese title, but Garou Densetsu translates to Legend of the Hungry Wolf.
I suppose if Fatal Fury is recognized somehow as an official title and not simply a bastardized Americanized title then I can live with that.
Either way, both tags need not exist.
Updated by Log