Older games worth playing on PC?

So right now it seems like the most active fighting games on PC are SF6, Tekken 8 and GGS, and no other games come even close (at least according to Steamcharts).

I'm a newcomer to fighting games, if we don't count Tekken 3 back on the PS1. I've been enjoying SF6 online, but was wondering what older games are worth playing even though the online play is essentially nonexistent. There's a bunch on Neo Geo that I've been thinking of trying out. I bought the 30th anniversary SF collection but there's like 40 active players and most doesn't seem to go online.

What's your recommendation? Maybe even an older title with an actual active online playerbase.