I've had a fun with my 3v3 arena group and our highest rating was 1700 (not that good but decent)
Healer: For a healer I would suggest a paladin, human prefered for perception but not needed. Priests are good because of psychic scream and shield but paladins heal fast with flash of light and barely takes any mana + divine Shield.
DPS: 1: Hunter: Has flare and ice trap
2: Combat Rogue, Or Feral Druid, OR Arms Warrior
Strategy: First off it's good to be in vent for arenas for fast responses. Usually take out the cloth wearer or the highest dps class. Have the hunter pop a flare and ice trap, then have the healer stand on the ice trap in case of ganks. Theoretically you take out the cloth wearer first because if you dps fast enough the healer wont have time to heal and if you have an MS warrior (arms spec) it should be cake then move to the healer and then the other dps. If you have a rogue try to sap one of them. As the healer if you get polymorphed only bubble if you see your teamates health get below 75% and if not then bubble if you get sheeped a second time after the first. DO NOT bubble if you get ganked by a rogue or anything if you are stunlocked, this is common amongst paladins because they panick.Don't panick Wait till you are able to cast spells and stun the ganker, then heal yourself.
Hope you liked it = D