Black Mage.

I have a number of favorite episodes, but the arc that sticks in my mind is the one where they find out about Matoya and Bahamut's "relationship."

Theif-"Worlds are colliding"
Matoya-"Usually three times a night!"

Oh, and the episode entitled "Criminal Intent"
White Mage- "This hammer will be introduced to your anatomy in a way that is neither comfortable or sanitary." Poor Black Mage.