Fire 2 and blizz 2 have different role, fire 2 allows to do AoE without take risk far from the group, when blizz 2 make you go into the melee.
if the monster don't have AoE Blizz 2 is better, if they have AoE around them Fire 2 is the trick.


if you allows me one second for come back to AoE vs 1 target, he is right, when your parseer give you the dps, is the damage done to all the target while x time... more target means more dps, but the hp pool stay the same, since you hit all the target at the same time.
like it was said, the break point for make the AoE be better is 4-5 monster, below is not worth... only summoner can deal AoE damage efficiently, since it spreads him dot.
finally, don't forget you are in a team, sometimes you will need to think as a team more than a DD, if you do AoE, means the healer will need to use more mana for keep the tank up, means the tank may need to use CD or make it jobs a pain like chain flash/overpower burning either them mana or tp for kill the pack without loose the hate.

a good DD do damage without take hate and without die ^^

but that another subject ^^