I've got 2 teams going at the moment,one is full Arcane the other is full Frost with a Frost DK thrown in a point/tank
For speed you can't beat Arcane (although i am running x5) and can Barrage most thing down to 15% finishing them with an Arcane explosion.
Frost is great where you need less mobility and CC is more important,say indoors instances ect.
So I would say if your Q levelling go Arcane,but if your looking to boost instances frost is better.
GL