I say that making a 2D fighting game is easier than a 3D one, but if you wanna go for the 3D... The thing is, I belive most 3D figthing engines are owned by softwarehouses and not open to the public, I could be wrong though. First, have you ever considered using something like Valve's Source? There is a fighting game made on that, even though it is a shooter engine (hell, I've seen a rally game made with the Quake engine!).
If you really aren't into developing something so complex, you could find those customizable kits for fightiing games. I've seen a couple of those for 2D fighting games, Chaltab has mentioned a 3D one, but I don't think those are really that good...