Quina's the best.

Capture a bit over a 100 frogs and your frog drop is dishing 9999 every time.

Mighty Guard and Auto Life as mentioned before, are priceless. Any character can do 9999 damage or near that amount with the exception of maybe Steiner. But not only does Quina do 9999 every time, but it has some very valuable assist spells as well.