Warrior of Tera the number one damage dealers for single targets. Damage can throw fast, but when it involves a group of monsters, they will not kill them as fast. Also need to try out how their "tanking" is. Archer going with the stereotype of being the crowd control. With traps and just having long range kiting skills they are perfect for it. Able to dish out a good amount of dps, but also being able control the crowd when the mobs are just to plenty.
Priest are just needed. No matter how good your skill is in blocking or dodging, you will eventually get hit, that is where your friendly neighborhood healer steps in and keeps you from death. Not to mention the buffs they provide. Mystic we are not 100% sure on how this class(buy tera gold) just works yet. We are assuming he's a Sorcerer/Priest hybrid of sorts. Being able to dish out damage and also buff the party.