Call me a casual but I've never not had fun with the Super Smash Brothers series. From 64 all the way to Ultimate, I can't name a game I didn't enjoy in at least some capacity. As for more "traditional" fighting games... it's a tough call, but I genuinely enjoy Dragon Ball fighters. My first was the very first instalment in the Budokai series, but I think I dropped off around Budokai 3.