The battle system isn't directly related to the way in which the characters increase in power, it would have been no problem making a game which used experience points and the CTB system. Besides, AP is basically Exp. points and AP in one in FFX. Just to have cleared that up.

I prefer the ATB system, because it's more action oriented. It forces me to think and react faster, and I like that. It is much easier to use spesific tactics with the CTB system though.