For the record I voted: Zidane, Quina, Eiko, Aramant.

Zidane for Steal (essential for an item collector like myself) and with his best weapon his attack is up there. I never really bothered powering up Thievery. His Trance is also pretty good.

Quina is versatile and has the easiest to power up 9999 attack (Frog Drop). He/she also comes with a variety of other useful spells like Auto-Life and Angel Snack which makes him/her easily the most useful character in the game.

Eiko is by far the better summoner/white mage combo. She is more white mage than summoner, but her limited amount of summons just as good if not better than Garnet's.

Aramant has a nice variety of abilities in his Flair set, including buffs, cures, and damage. I never use throw but that's not what makes him great.