Apparently you guys are not aware just
how much better for PvP unholy is, which kinda explains the backlash when I questioned the fact that this was a PvP guide using frost spec.
I don't know how much any of you play your death knights in PvP, but in case It's not that much, I can tell you that death knights primary burst ability is
Death Siphon.
Death siphon out-damages any other ability death knights have
significantly. Death siphon is in other words the best way
by far to spend a global while bursting.
Now, frost death knights has two permanent death runes (instead of blood runes) due to
Blood of the North. Which limits the maximum amount of siphons they can cast in a row to two.
Unholy death knights gain access to
Reaping which allows them to set up 4 death runes at a time, and do a much more significant burst.
And I won't even go into the details of how much being able to
control your ghoul helps in PvP.