As with the one I did in your FF4 thread I'm doing them by gameplay. Here goes...

1. Rinoa. Angel Wing + Meteor + nothing else but defensive spells to buff all her other stats = dance all frakkin' night. It almost seems wrong that I should like a character I can leave to stand around and do 60,000 damage per round without me pushing a single button but given that this is a pretty damn easy game once you learn to break it, then to me it's just buying more time to get the best use out of...

2. Selphie. With Rinoa spamming Meteor you have plenty of time to rifle through her Slot command and use whatever you want. If you need more time, you can always use...

3. Quistis. Her Blue Magic is extremely versatile, though it can be a pain to locate it all. Once you do, though, she's as overpowered as the other ladies.

4. Squall. Well he's mandatory for most of the game so it's just as well his Renzokuken does very good damage. I always sigh when he runs directly at the camera though because that's how you know he's only gonna hit four times ¬_¬

5. Irvine. And even though I ranked him fifth I still find him very useful. The only downside is having to have ammunition in your inventory. Using Dark Shot on bosses and ruining their crap is awesome though, and very nice to have if you haven't got Bad Breath for Quistis yet, but if you're like me you'll get it out of the card game right at the beginning :P

6. Zell. His Duel is just too time-consuming. As much as I found it quite fun to do the first few times, I got tired of it after a while, and while it has the most reliable level of damage-per-turn output out of anything in the game, it's hindered by the fact that alternating the same two attacks for it is a real chore. He's not a bad character, I just can't be arsed to execute his limit break any more.