I'd say that if you want to try some old fighting games for free to see if any of those you'd like to play more, there's always Fightcade.
Seems that you haven't played online fighters in a while though if your last game was MKX - I think both SF and Tekken have solid netcode and playerbase, although both of their current games seem to have some sort of oddities with balance at the moment, but I digress.
I would like to be able to tell you from my own experience, but it has been a good while since the last time I played Guilty Gear Strive online, and haven't ever had access to online SF6 or T8 - so the newest games I've ever had a chance to play online were USFIV and [also loooong ago] Tekken 7.
In any case though, thanks for reading and for your comment :]
RE: Returning to Ultra Street Fighter IV: A long time awaited comeback to the streets [ENG/ESP]