So, I no one really debates over this even though hero vs hero and mage vs mage and the like are very popular.

Personally, I have to go with Fina from Skies of Arcadia. It's really rare for the healer to be the charather that breaks the game, but I mean. Lunar Light. It always goes first, it cancels the enemy turn, it revives all dead party members, it removes status, and it fully heals. And on topp of everything it uses SP instead of MP, which is renewed at the end of every turn, so you don't even have to worry about ever running out. And it's not even like she's a weak charather earlier in the game, since her team regenration ability (lunar blessing) earlier on trivializes the fire and jungle dungeons. Her only real downside is that her game has low difficulty anyway and you have to sit through the animation.