Mage: Highest damage to multiple targets fast, low survivability.
There are several opportunities with traits to boost Mage AOEs depending on what you want to do with your character... but only two of the AOEs are implemented thus far(the close range ones) so the true effectiveness of the ranged AOEs are unknown (at least two of them in the works). It's possible once all spells are in that the Ice trait path (provided u pick the correct traits) will have 2 AOEs (one ranged, one close up) that will both damage and freeze targets with a faster than nontraited cooldown for recasting.. very poweful
There are also some otherwise previously uknown spells referenced in the traits that may end up being AOEs (or not). But keep in mind.. you definately can't be the one taking the damage from these mobs.. your damage mitigating abilities eat up your mana like crazy (there is actually a trait to reduce this mana cost, and another to help regen mana in general).. and when your mana is gone you become pretty useless.
Fighter: Engage multiple mobs, do alot of damage and effectively mitigate damage in a group setting.
From the point of view of the fighter - you can wear a shield, mail armor and with traits increase the effectiveness of Heavenly rumble (AOE that causes damage plus slows mobs for short time), as well as skull splitting (deal damage to two nearest opponents) and/or give yourself defensive buffs. In addition you have an AOE aggro taking skill, an AOE that decreases enemy damage output, an AOE "fear" skill (causes enemies to flee temporarily), and an extremely high damage skill with very short cooldown (fatal turnabout) that only works when the chips aren't in your favor (such as when your fighting multiple enemies).
Templar: Take on multiple enemies.. and not die. Solo.
Templar has the highest natural defense (shield/mail armor/buffs), the ability to heal themselves in a fight, and the ability to regen mana as fast as it is lost (if you play deliberately and not button-mashing style). Has an "average" damage output, but infinite survivability. The only true stand alone class. Others can expand on this better than I.