Soku. So much fun, so many memories. It also happens to be the only touhou game I own a physical copy of. Its simple enough that people who don't really play fighters can get into and have fun, but also so complex that once you learn the game battles can become stupid awesome. A great night of playing soku with friends can get me so pumped up!
Other than that I dont really play other fighters because the communities for them tend to suck (and im also pretty bad at them). I used to play the hell out of some soul calibur though.