Predators are damage-dealers who are relying on their main cannon. Some Predators also act as assassins and feature cloaking devices or traps.
Titans are masters of survival and the protectors of the team. They can absorb a lot of damage and often draw or reduce enemy fire.
High-Techs are designed to deal a lot of damage quickly with their abilities and often feature devastating area-effects.
Supports usually don’t deal much damage by themselves. They are either buffing and repairing their own team or debuffing and disrupting the enemy one.