In big outdoor situations, where I have plenty of room to run around and pick up mobs without getting hit too much, I do like frost better since you have the greater control with all the snares. It's much better at keeping a group of 20 even con mobs, which will kill you fast, at a distance. However, in a situation like this (couldn't have toons follow or they would auto-agro everything, so I had to make a loop and come back) where I'm taking a few hits, I find that fire is actually faster. You can see the explosiveness of the actual AOE, and maybe you can't tell from the video, but I was usually at 50-75% mana after I finished which means a quick drink and I'm off to the next.

In short, I feel that fire is more efficient given these circumstances.

Plus, it's more fun!