I love fighting games, and by far the greatest game I've played is Street Fighter Alpha 3. Tons of characters, lots of game modes, excellent balance between (most) characters, and a battle system that has been refined for the past decade or so.
I've tried almost every fighter you can think of... Virtua Fighter, Tekken, KOF, Samurai Shodown, MK, DOA, Guilty Gear, Street Fighter III and tons more. (Side note: You're all gonna hate me for this but I found Soul Calibur to be EXTREMELY boring, dunno what's with the hype) While most of the games mentioned are indeed fun and great games, nothing has kept my interest like SFA3. Maybe I'm just one of those die hard 2D fighter fans.