heh.....looks like I voted without reading!
so I assumed it was favorite battle system, and voted for X!
Of the ones I've played the battle system I disliked most would have to be XII.
Man, I was so excited about XII.......and was severely let down by that foolish gambit system.
I wasn't that fond of IX's either. Learning abilities from equipment seemd silly to me, and some of the abilities in themselves were just foolish