I prefer arcane/fire because I can choose between sustained damage with scorch/fireball or burst damage with AB spam depending on what I feel is necessary. Also with Arcane Subtlety you can choose between high aggro or low aggro rotations if you are in a threat sensitive fight, or if your pug tank sucks.

On your frozen mobs, add an Ice Lance with your Frostbolt to get two crits in one.

For the deep frost talents, the Winter's Chill talent stacks up automatically on my main pew-pew Frostbolt to allow all mages with Frost spells to get higher crit rates. The Improved Frostbolt adds crit aswell.

For threat, with Frost Channeling I can get less threat off my main spell school.

Frost DPS needs to be maxed out with the Water Elemental if possible.

Arcane has higher burst damage and stat change, Fire has highest per-shot damage and DoTs, but Frost has most sustained criticals and mana-efficiency. This all balances out .. with Frost the option is you can afford less upfront damage because you live longer. If you die, then your spec doesn't matter, you are causing 0 DPS anyway.

However, the reality is the main group DPS probably won't be from a mage spec anyway, it will be Warlock or Hunter .. !!!