Just because I like to run numbers.

OK! So. Based on general guides for all specs of mage, I decided to blow some gold and run some tests at level 65.

I did
fire (Crit at 28%, Haste at 20%) Molten Armor
Arcane (Haste at 26%, Crit at 24%) Frost Armor
A. Frost (Haste at 29%, Crit at 22%) Frost Armor
B. Frost (Crit at 28%, Haste at 20%) Molten Armor
Running proper rotation (given I am a low level and don't have all spells)

Single Target DPS
Fire - 1700~ No mana issues

Arcane - 2100~ burning mana, 1600~ conserving with good rotation keeping arcane charges up at 6 and missile on use, 1800~ Generic rotation, Missiles on double proc, barrage only at 6 stacks of charges

A. Frost- 2200~ Using basic rotation, ice lance on proc, open with frost orb to get like 4 free super lances. No mana issues

B. Frost- 2600~ Using personal rotation, Open with 4 frostbolts then Frost orb, Ice lance on proc. Still no mana issues

Arcane has been dubbed useless for ST at this level. Fire is beast, but is way too RNG based, frost Works either way.

AoE - Just basics, no numbers because there is no means of a control

Fire - beastly, and scales WAY up with more than 5 mobs

Arcane - AE spam? YES! It charges stacks of arcane charge, and when at 6 use Barrage to do a shit load of AoE, This is the best if you are going to have to burn down 10+ mobs, but dont forget that at most arcane barrage hits 7 targets (your target, then up to 6 additional for 50% less damage)

Frost - Ice lance can be glyphed to hit an additional target for 50% damage, but that hit is still a 4x damage plus crit (well shatter gives it a +50% on top of base crit) (8x) and you can also just blizzard if there are 4+ targets, it does damned good AoE also.

Oh, wanna know what Ice lance will do in PvP? Well... Lets say you have 30k Spell power, it will do a base of 55k (as crit) or 27.6k as non crit. Minus PvP Resilience (base of 30%)