Warlock Priest Or Mage?

I've never had good luck with warlocks so I can't tell you much about them but a mage is a really good dps. A priest sometimes has to be ready to heal because a lot of healers leave and they get to be hard to find so the rest of the group is going to want you to have dual specialization and heal the party. at least with a mage they just expect water and damage. try them all and see which one you like. It can't hurt to experiment.