Isn`t arcane terrible mana inefficient? Personally I would go for fire. Since when your questing (not instances) youw ill mostlikey nearly oneshot mobs so big damage is usefull. I think fire helps in that.
I`m pretty convinced that frost isn`t a way to go tho. No need to slow things.

But personally I allways say people should spec the way they like to play. Eventually you can make it work.