I mainly find myself sticking to newer 2-D fighters, since most 3D ones like taking after street fighter. Blazblu, guilty gear, skullgirls, and P4A. I like the speed and lightness of these games over the controlling a brick of street fighter or tekken (though I love tekken 2). I would have to say though if I were to pick, skullgirls and P4A tie. They both feel different enough from other fighting games, even ones that move just as fast. It probably helps that persona doesn't go by standard fighting game logic of high punch, mid punch, low punch. Going instead for a standard attack, a long reach, and 2 persona buttons.
An while skullgirls keeps the standard scheme it uses it in a different manner due to how the characters control. No one controls like one another, and they all feel super different when compared to other fighting games. I'm not hard pressed for examples, but to many come to mind for me to pick one to put down. Like how valentine works with her needles to cause lag, poison, or slippery controls. Ms fortune's head being the best little troll you can possibly have on the field if you know how to work it. Peacock.. being peacock.