Dwarves are the preeminent
The Guardian should be leading any exploration of instances, and is best deployed in front of the fragile healers and nukers, but close enough that he can turn and reclaim La Tale Ely from them without moving too much. Attack slowly around a Guardian and let him attack first, so that he can build up and retain aggro - it is a lot difficult to take enemies away from someone else than it is to attract and hold them in the first place. Dwarves are the preeminent Guardians, but Humans can also tank perfectly well.