Weird Question, AOE is better depending on the number of targets...
since most of the trash groups consist of at least 3, AOE is better (for me)
furthermore:
I'm an enhancement shaman, so I use my AOE (fire nova) to give me my elemental devastation buff at the beginning of the fight (9% crit is nice!).
And:
I always put all my totems down, so (in a way) I always AOE.