Prerequisites: Lv.2 Wizard
Weapons: Rod
Armor: Hat, Clothes, Robe
Time Mages aren't very effective unless you spend a good deal of time developing their abilities. Many of their spells almost always miss. Their meteor and demi attacks are devastating but in the time it takes to get these two spells you could be building up a better job.
Prerequisites: Lv.2 Time Mage
Weapons: Rod, Staff
Armor: Hat, Clothes, Robe
Summoners have a combination of healing and attacking spells. Their spells tend to be more effective than both the Wizard's & Priest's since they cover a wider area. Also you don't have to worry about killing your own units or healing the enemies as the summoner's spells only affect the proper targets.
Prerequisites: Lv.2 Archer
Weapons: Knife
Armor: Hat, Clothes
Aside from their Move +2 ability, thieves aren't very useful until the latter half of the game. There are a great deal of powerful items that you can only get by stealing from enemies, and such units don't show up until around Chapter 4. Also, their Secret Hunt ability lets you trade in poached monsters for items at fur shops, which don't appear until Chapter 3.
Prerequisites: Lv.3 Monk
Weapons: Sword, Axe
Armor: Hat, Clothes, Robe, Shield
Geomancers attack using the various elemental powers around them. Even though their attack power is above average, they lack any especially-effective techniques.
Prerequisites: Lv.3 Thief
Weapons: Spear
Armor: Helmet, Armor, Robe, Shield
A Lancers only attack ability is the Jump function, which is not only powerful, but also temporarily prevents damage from enemies since you're in the air while the attack is charging. The spears that Lancers use allow them to attack from two spaces away. Lancers have very high HP and attack power which makes them an excellent job for the latter half of the game.
Prerequisites: Lv.4 Monk, Lv.3 Knight, Lv.2 Lancer
Weapons: Katana
Armor: Helmet, Armor, Robe
Samurai have high attack power (especially with the Two Hands ability) but their HP is relatively low. Their katana skills are really only effective when surrounded by enemies or party members. Since the blades tend to break occasionally, having a Samurai in your party can be quite expensive.