Who knows? Something like this at the moment:
Battle Garegga - This is probably my favorite shooting game. Not even sure I could point out why. Nice feeling controls and awesome music. The bullets are pretty hard to see, which somehow adds to the fun.
Magician Lord - Will probably always remain my favorite Neo Geo game. Great music and the visuals and game itself are quite unlike anything else on the system.
Street Fighter Alpha 3 or Third Strike or maybe just regular ass SF2WW, or shit, maybe even ST - all of these had a massive impact on me. Would probably depend on the day as to which one I would pick.
DDR A - Gh3y, I know, whatever - fact is, DDR was the first new and fascinating thing in games I had seen for a long, long time in 1998 or 1999, whenever it was. Still hard to believe how fun this game is, and A is, to me, a perfect version of the game.
Ketsui - Played this like there was no tomorrow the semester that I studied in Japan, and for the first year or so after I moved there. There actually turned out to be many, many, many tomorrows, all full of Ketsui. That boss music too...
Esprade - Still the only Cave PCB I've ever owned, probably will remain so. Got to the last boss, but never got the 1cc... Not even sure I'll ever try again, to be honest, but really awesome memories of playing this all night in the basement at the old crib.
DOJ - To me, Donpachi is what really ushered in the next gen of shooting games, and DOJ is what ushered in the next level beyond that. Pretty insane right outta the gate, and never really lets up. Second level music still strikes me a certain way... Maybe it's just that I suck so bad that whenever I get to hear it, I feel moved? Dunno.
Batrider - This game is just insane. Great music, really interesting characters, pretty tough one too.
Real Bout Special - It's kind of a toss up between this and some other FF games, but had great times playing this one with my homie when he got his MVS in the early 2000s.
R Type - Again, the music here seals the deal, but this game is just something else. The SMS version was the one I was first familiar with, then an arcade that I worked at in my late teens had it and I spent many a slow day learning this game. Great memories.