If you want to be more of a leader and be up on the front lines taking the hits, choose warrior. If you want to hang back and deal damage, then pick black mage. White mages also hang back, but they're almost entirely support magic i.e. cure, shell, protect, etc.. Thieves don't really come into their own until around lvl 15 when they get sneak attack and treasure hunter, but can be very good for gil farming. Monks have a lot of hp, but not as much def as warriors. Choose this class if you want to stay on the front lines, but not have to take charge as much as a warrior. Red Mage is kind of a Jack of all trades. They can fill almost any role in a group. They can use their decent physical attacks to stay on the front lines, or they can hang back and take the role of healer or cast black magic for damage.
