King of Fighters XI: arguably the best king of fighters game. great graphics, lots of characters.
A rough tie for my "favorite KoF game ever," along with 2002 Unlimited. If they ever do some kind of XI "UM," it would surely surpass them both; although it's hard to imagine any other KoF doing that; and doubtful it would happen with XIII in the works (which looks at least like it might be a good standard-faire game, although pretty-looking).
And just because GGI isn't as popular as something straight-forward as XX or Accent Core doesn't mean it's not a better game. People are just too lazy to really figure it out, it has too much depth. Can AC do dual-plane fighting? Dramatic battles ala SFA3? A character with move customization? Cheap, simple instant-kill moves are no substitute for substance like that. Although admittedly, they are kinda funny the first time or two you see them.
Sorry man! GGI > GG*