IV
It's the most stable, linear story. Not a huge amount of twists, but enough to keep you interested.
It flows really well for the most part (unlike some of the others) so you never really get frustrated with it.
I do have to admit, the battle system in this one didn't really make a lot of sense to me for the longest time, what with the damage and all the damn multipliers. The best part about that though is you can simply ignore it and equip the best stuff you have and be fine. I did finally dive into what makes the game tick, and now I have retardedly OP characters in a save, but it took some work to fully understand.