Lately while leveling black mage I've had a few groups where I would be casting my aoe sleep at beginning of pulls with 3 or more mobs. Someone would tell me to sleep less and dps more.

Another group someone said to sleep less and AOE dps. That group 2 of the members got to arguing about the fire 2 AOE damage, and I got totally confused on how I should do my job. I tried to just AOE fire 2 everything, but that didn't seem as effective as single target Fire 3 + Fire. That one guy was also arguing that sleep just delayed the run also. Also the tank didn't mark mobs at all, so maybe that's a indication to AOE dps?

I'm very close to reaching level 50 black mage, and still not really sure when to AOE dps or Single target DPS. Can anyone give me any tips on how to know when to single or AOE dps?