Best PvE Dungeons LvL 49 and 59 TWINK

Hello. I am interested in helping out people by being a twink at the level of 49 or 59, not sure yet and that is why I am here asking you for some tips before I make one. It's supposed to be a spell caster except HUNTER, cause I do not wanna play him and I have no clue what class would come with the highest damage done to the npcs in dungeons. Some of the players have already tried to give me some tips in the game, however I would like to make sure they were reliable source of information.

So what casters should I consider as the best at the level of 49 or 59 in dungeons?

Mage
Druid
Shaman
Warlock
Priest

I would recommend picking a class that can also heal, that way you can fill two roles if needed, so there's less of a wait to get into a dungeon. Other than that, just pick a class you find fun to play. They're all useful if played well.