IMO Frost is the best leveling spec due the the high survivability. While leveling frost i could probly count on one hand how many times I died. Raids are a diffirent story. My frostbolt dps is nice but being fire before I know I could pull some serious DPS with fire. I tried out Frostfire for a day or two but was disapointed in my DPS mostly, I think, was due to the low crit in my gear. It all depends on what you plan on doing more I guess and if you dont mind respecing for raids. Hopefully Blizz will come out with dual specs soon. It will make mage life a lot more simpler.