The peerless white mage

[Raistlin]

Despite the fact that I'm not exactly fond of her, I'm surprised that Aerith is not an option.

I voted 8-bit theater's version as a cop out, because I just didn't care for most of the dedicated white mages, at least as characters. It sounds like Minwu was interesting (and notably male in a female-dominated role), but I haven't played FFII. FFI's White Mage would probably be my choice anyway if I had to pick from the actual games, as he/she was fairly useful and had the added benefit of not being annoying (the lack of character development/dialogue does have some perks).

[Del Murder]

I feel Rosa was the most useful as a white mage to the party. She saved my ass a number of times and a lot of battles simply could not have been won without her.

Yuna is the most powerful though, since her summons can pretty much solo every battle in the game.