my apologies. duplicated thread, refer to fighting on a budget?
Skullgirls and KOFXIII are on Steam as well, and with both of those games, the Steam versions are the definitive versions. Look at http://steamcharts.com/ to see how many people are playing each game.
Alternatively, you have SFxT, SF4, Injustice, and MK9 on Steam as well, but I personally don’t play them. We don’t have GG, BB, or P4A though.
You can also look into GGPO if you are interested in playing some of the older arcade games online.