Warriors are unique in that we have three stances and there are some stances that serve better depending on what you are fighting. Below is a general breakdown of what stance you will want to be in when fighting each class when referring to main stance have means the stance you find most effective based on aion gold. It is usually battle stance for arms spec and berserker for fury spec.
Warriors are unique
Here list the classes and the stance and reasons respectively:
Rogue: Battle Stance / Overpower FTW
Hunter: Berserker / Intercept, because chasing a hunter is quite possibly the worst thing ever.
Mage: Berserker / Intercept, massive DPS to blow through the pajama armor
Warlock: Berserker / Intercept, massive DPS to blow through the pajama armor.
Shaman: Defensive, then back to main stance, Berserker / Disarm to lessen DPS, intercept for wolf form.
Druid: Main stance, Berserker / Beserker for intercept when they run away as a wolf.
Paladin: Defensive, then back to main stance/ Defense for disarm, a pally without his main hammer, just is not a pally at all.
Priest: Main stance, Berserker / Beserker for intercept.
Warrior: Essentially this comes down to who can play better and has better gear.