Since he/she didn't mention that about aoe grils I always considered that single target can finish by herself while aoe can't.After MiqDoloran's post I realized that I though earlier of one scenario (all enemies are equally strong) while that isn't always true. After all I said:
Now after this discussion I agree that mostly it's better to have aoe first but I don't think it shouldn't be mentioned that there're situations where it isn't true.