Fighter/Knight - Too expensive and equipment dependant

Thief/Ninja - Not worth being handicapped half the game for a subpar Red Mage later

Monk/Master - No customization at all, pretty boring

Black Mage/Wizard - Offensive Magic sucks and I hate status magic

White Mage/Wizard - Items will do most of their work anyway and I hate dealing with limited MP

Red Mage - Has all the strengths and weakness of the BM, WM, and Thief rolled into one