The warrior class uses a sword and shield and has high defense, but weaker attack. Warriors are your tanking class and have many debuffs to help weaken the enemies.
For more information on the Warrior Class, click here.
The champion class uses a sword.They tend to have high chance of dealing a critical hit and have stronger physical damage than those of warrior's but very poor in defense compared to a warrior. Therefore champions are the damage dealing class.
For more information on the Champion Class, click here.
The mage class are basically the killing class in the game. They use a 2 hand wand, and only to focus on one thing, killing. Has many AOEs and if it has the right pet and skills can deal massive damage and survive powerful enemies.
For more information on the Mage Class, click here.
The priest class is the healing class, Effective in Faction vs Faction, Party Quest etc. They have damaging spells but not as powerful like the Mage. For more information on the Priest Class, click here.