My first choice would be Real Bout Fatal Fury. Some people don't like the first version in the Real Bout series, but I believe it offers style never before seen on the Neo-Geo. The ring-out feature really made the game standout; it felt like the FF series took another step in its evolution.
The graphics are gritty in comparison to the bright, pastel colors in Special, but they ooze with old-school personality.
Sound Beach! I'll never forget the time I knocked Blue Mary into the ocean at Sound Beach; she slid off the pier, fell into the water, and then returned to the surface topless. lol I was shocked by this for the simple reason that SNK was so anal about having blood in their games, I was never expecting nudity to appear uncensored.
Let's face it people -- RBFF has some of the best tunes this side of the community. RBFFS and RB2 also had memorable music but none of them can hold a candle to the music in this game, bar none.
The in-game characters were also drawn differently with a style that matched the atmosphere perfectly. Yamazaki was at his best in this game -- he was cool, well dressed, and he wasn't 'goofy' like he is today.