Arms warrior-restoration shaman and frost Mage
warriors: Arms warriors have the debuff abilite callled mortal strike, this will reduce the targets healing by 25% which is awesome against healers, also with their rend and deep wounds talent point their bleed abilites are nice it does a very good damage over time on the target. They also have sunder armour it reduces the amount of armour on the target, less armour more damage on the target, They also have thundeclap Which can slow down the enemies attack speed by 20% is pretty good espically againsts rogues. and they have battle shout which increases the agility and strength of people around you and you also gain rage from it.
Shaman: Restoration shaman, are amazing one because of earth shield, because when you lose health it heals you, with 10 chargers ( if i remeber correcrtly) also they have nice remover called cleanse spirit which is good against warlocks. They also have totems, which are amazing, they have totems that can slow you down by 50% , have totems which increase your agility/ strength, have totems that can heal the whole group, have totems that can do damage, casting wise, and have a totem that can increase your spellpower by 6%. they can also use purge which is amazing, it can get rid of any magical things on the enemy for example, when you use purge on a priest it gets rid of their shield, and their's no cooldown, and they have windshear which can stop the enemy from casting. and also ghostwolf, for getting around the arena better.
Mage: frost mages are king! one because of the water elemental pet, it can do damage and also have a frost nova which you can control, they have a good attack called frostbolt which can slow down the enemy. they have blink which can thrust the mage foward and can break roots, frostnova and i think HOJ. they also have silence which is good against healers and damage casters. they have polymorph, which is like hammer of justice expect you gain health while your in that state, and you also turn into a sheep.
This info might be a little werid, but this is the info i have experienced, from doing arena to bg's and duels. also, a lot of the info is my opinon so before you rage attack, this is what i think their good for.