I would take the Red Mage if he could equip the fire/ice shield/armor (I give the opal bracelt to my black belt). I find the hardest part about this game is your armor equipment management. You only get 16 slots for armor, and yet there are times where you want different armor eq for different situations, but don't really have the option to switch because you're restricted by how much you can hold. I just find it odd how the Red Mage can equip heavier armor/weapons than the Thief, but the Ninja can equip heavier armor than the Red Wizard; it truly shows how the Red Mage is a great early game character and the Red Wizard is a crap late game character. And no, the Red Mage is only the second best fighter for the early part of the game. I find that the black belt is the second best fighter after level 10 or so, and the best fighter after level 24 or so.

Anyway, the best thing about a Red Wizard, is that he can cast both Exit and Warp (good for the last level), and if you want an all melee party, then he's better to take than a BW or WW.