WoW Priests

Priests play a huge role in both PvE and PvP. They bring an amazing buff called Fortitude, which increases the hp of whomever it's put on. Priests have a very wide range of non-casting heals (they are instant) in their arsenal. These abilities allow Priests to focus on other things during the fight, such as mana burning (taking mana away from the opponent targeted) and dispelling, either taking buffs off opponents (like Fortitude) or taking off debuffs (bad buffs) on his teammates. Priests have three different specs (various areas to choose abilities) that are all viable in Arena.
             
Holy Spec is the best Priest spec for healing as they gain many buffs to their heals through talents. Discipline Spec is what most 5v5 Arena Priests use as it gives the Priest many Defense abilities and because of this Discipline Priests aren't often targeted (the person the opposing team tries to kill). Discipline Priests also receive a quicker mana burn, which helps stop the enemy from healing long term, and better spirit regen, which allows them to be efficient longer into the fight.

 

The last spec that Priests can be is Shadow. Shadow Spec is vastly different from the previous two because the Priest primarily does damage in this spec. They have abilities such as Mind Blast and Mind Flay which do a very high amount of damage. Shadow Priests also have two unique abilities Vampiric Touch, which gives hp back to all teammates when damage is done to target, and Vampiric Embrace, which gives mana back to all teammates when damage is done to the target. All of this and the Priest still gives Fortitude and Shields to its team. The downside to a Shadow Priest is that when it's in damage form the Priest cannot heal at all. Shadow Priests also do not get the defensive abilities that holy/disc Priests do and they are very squishy (easy to kill) and are usually targeted first. Because of the variety and the amount of Priests on Arena teams they are regarded as one of the best balanced classes in the game.