If only Kingdom Hearts 2 would have been mentioned on this list.. Easily has one of my most favorite battle systems of all time, and I wouldn't mind seeing Final Fantasy take that turn at all, but that isn't what we're discussing here, is it?

In terms of battle systems, its a tie between the X and X-2. As much as I hate them both with a burning passion, the battle systems won me over easily. A cross between these two battle systems, with more control and maybe even a kind of multiplayer aspect (Even if that is going to far out of the questions) like Secret of Mana, though I doubt it'll ever happen, would probably be my ideal battle system, even if it does cross swords with Kingdom Hearts 2, THE defining action RPG. For me, anyways.