I've been playing fighting games since Street Fighter II came to arcades. I reluctantly played them at first. I eventually grew to love them. I'm a Street Fighter player at heart, with my favorite being Super Turbo.
I also grew up with Neo Geo arcade games. Samsho is my absolute favorite fighting game. It's nothing but fundamentals. It's the one game that will confirm you either understand or don't understand how to play fighting games.
I think Killer Instinct is the pinnacle of Street Fighter-style fighting games. It has execution, knowledge, and reads all in equal measure. Moreover, Killer Instinct gives you not a single moment to rest on your laurels. Whether you are on offense or on defense, you have decisions to make. Play KI.
However, I'll play just about any fighting game casually. I also don't exclude certain games from the genre like Smash or Fantasy Strike. I think both are fantastic fighting games in their own right. Hell, I even include tabletop games like Yomi, Unmatched, BattleCON, and Exceed.