My favorite series is King of Fighters because I like a lot of the characters, but gampleay-wise I prefer Fatal Fury. I find the that the Fatal Fury games tends to strike a really good abalance between ease of controls and a slightly slowed down experience that makes them pretty newbie friendly.
I also like Guilty Gear, Darlkstalkers, Street Fighter , Marvel vs Capcom and Samurai Shodown. Though I am pretty ambivalent about street fighter 4 (I prefer the Alphas). I've got Virtua Fighter 4 and it seems awesome but it takes a lot work to preoperly get into and I am not there yet.
There are also quite a few games I still want to try out Last Blade, Matrimelee, Waku Waku 7, The Capcom JoJo games, Kizuna Encounter/Savage Reign, Rage of the Dragons, World Heroes Perfect, Fighter's History Dynamite, Breakers Revenge, Deamon Bride and Aquapazza. (the last one has recently been announced as coming out here) So yeah I kind of like fighting games in general.