Off the top of my head:
Wizard
Elementalist: Frost Cloud is one of the best AoE’s the Wizard tree has.
Sorcerer: Ride bosses that can have a lot of AoE attacks.
Kino: Low damage, but the AoE is decent. Doesn’t do well with ranged monsters.
Cryo: It’s more setting up for AoE attacks than the AoE damager.
Warlock: I’m not sure, I never really played one, but people usually use this with Elementalists.
Cleric
Plague Doctor: Best Cleric AoE. You can pretty much spread poison to an entire room of enemies.
Inquisitor: Breaking Wheel spreads your physical attacks. It has less AoE than Plague Doctor due to longer CD, but still really solid and has really good damage depending on what you hit the Wheel with.
Bokor: Exploding zombies.
Miko: Hamaya creates a magic circle that can hit 10 targets at a time.
Sadu: Possession seems ok. Hits 14 targets maxed and immobilizes them.
Archer
Sapper: Broom Trap places a cycling trap that has good AoE
Falconer: AoE support. This class pretty much makes almost any class into an AoE class.
Swordsman
Doppelsoeldner: I have no idea, but I know it’s a popular AoE DPS choice for Earth Tower.
Not really experienced in Archers or Swordsmans, sorry.