Man there are so many, if I have to go with one being my favorite, it would be the Marvel vs Capcom series with 2 and 3 leading the forefront. But Street Fighter has always guaranteed a great gaming experience (my favs would be Street Fighter IV, III, and the Alpha series). Mortal Kombat revitalized the dying series with its latest iteration, which is awesomely addicting. Another fighting series I tend to buy is Soul Calibur with all of them being great in my book besides the latest one (Ugh! What a waste of money). Killer Instinct will forever be embedded in my mind with its fluid gameplay and ultra combos, man the way it felt to play Killer Instinct the first time, the button mashing leading up to big count combos i've never experienced before in a fighting game (this series had a battle with MvC for my favorite fighting game).. Tekken series is another solid one, with my favorite Tekkens being 2 and 3 (I love counters and chain slams lol). Then there was the SNK world of fighting, what a treasure trove of arcade gaming, besides the awesome King Of The Fighters, people fail to recognize the games that opened those doors. Fatal Fury and the battle of Joe Higashi, Terry and Andy Bogard vs Geese Howard, the transition between foreground and background fighting, if you wouldve asked me this question in the early 90s, Fatal Fury wouldve been my answer hands down. Samurai Showdown, Art of Fighting, even King Of The Monsters, were SNK games that were amazing at that time period (I spent a lot of quarters on any Neo Geo machine). Then Capcom's world of amazing fighters, Rival Schools, Darkstalkers, Saturday Night Slam Masters, Star Gladiator and so forth, always held it down.. And finally we have the Guilty Gear/BlazBlue type series for the hardcore fighters, I just cant forget to mention them too..