The Apprentice's towers focus on the elements.
The Huntress has traps which detonate upon impact or by using the Detonate Trap from the Wheel (default Middle Mouse button on PC).
The Monk uses auras that deal damage, or support the other players.
The Squire's towers are different from the Apprentice as all his towers deal physical damage.
The Apprentice and Squire have standard towers that deal damage to enemies that come into range.