If you're exclusively interested in PvP and don't care about anything else the strongest overall 5man is probably just 5 elemental shamans. They do a ton of burst and have massive survivability through high armor, grounding/tremor totems.

My issue has always been I just really dislike shamans in PvE. Though, if the dungeons continue being as easy as they are on beta enhance tanking with magma totems may be decent enough clear to try. Have to watch some streams of some of the higher level dungeons.