I'm digging the Red Mage in my current playthrough. Monk is the class where after I tried it, he's been a standard member of my party in every playthrough. I think Thief is the class I'll never get back to. Ninja's are pretty good, but not worth the hassle of lugging around a dead weight character life Thief. Black Mage is also not so great, but for the sake of nostalgia and loving it's design, I love having one in my party.