go frost becuase...

any other spec youl have to drink just becuase your mage is OOM
nice slow on targets meaning even some elites wont get to melle
replenishment mana regen so no one will ever need to drink
eas as hell to macro its just spam frostbolt.

Id suggest leading with mage as others already have, it'll mean your FB will hit first slowing the target and gives you access to all the mage utility aoe blizz etc