Sorry, been away a bit recently, sun is right. Dont raid as frost, it isnt worth the loss of dps for the minor repleneshment bonus you give the raid.
Frostfire is the best for mana conservation, followed by fire, and then deep arcane as the least mana efficient. Invert that list for dps potential.
I am fire right now, because until the next patch, the scorch debuff is the best debuff that can be put on a boss. Only one person needs to add the debuff though, so all our other mages are arcane. The debuff adds 10% to crit chance. My rotation is scorch to 5 stacks (2 casts with the glyph) then living bomb. Then cast fireball until scorch or lb need to be refreshed. When your pyromaniac buff goes off cast your pyroblast instead of fireball.
I would suggest you try fire spec, if you are new to magery, because its simpler, but arcane does have higher dps output. (which means im 2X as good as sun for beating him.

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Arcane is focus intensive, because the goal is to use all your mana during a fight. Typically you stack your arcane blast, and then use arcane missiles if the barrage buff is up, or use arcane barrage. There is no combo on arcane barrage after missiles any more, so dont bother casting it after missiles, waste of time and mana. Sounds pretty simple, but ooooh is it.
If you are doing arcane now, and arent often running out on mana, you arent doing it right. If you are running out of mana every fight, you arent doing it right, find somewhere in the middle.