Currently, my favorite currently would probably be Samurai Shodown V Special. All time would have to include SSVS, Garou, and probably any Metal Slug. I like the feel of a lot of the older titles but I couldn't really call one of them my favorite.
Since the semester ended I've been checking out games on my rOmZZ Box and I've just bought like 6 games for my MVS based on trying them out on it. I don't play the stuff on my xbox very often but I'm glad I checked these games out on it. I found out how awesome MD3 and Blazing Star are, and there's a certain charm to Kizuna Encounter and Breaker's Revenge that made me want them as well. I'm starting to like some of the fighters outside the SNK universe. Double Dragon pulled me in along with Matrimelee, RotD, and the others mentioned above. It's nice to play some different fighters outside of FF, KoF, and SF even if they aren't as refined.