Originally Posted by
raionyx
Frost is typically going to give you better numbers from a "pick up and play" perspective.
Unholy can do well, but typically requires a very specific environment/gear scenario to do so.
I am the only remaining Unholy DK in my guild, but I perform on par with all of the other DKs who have converted to Frost, and presently out-gear me by anywhere from 10-15 ilvls. That said, I have the Unholy Bracers, which are the largest DPS increase for Unholy, even after the massive nerfs coming into 7.1.5. Typically on most fights in Heroic Nighthold I've been in the top 10-15 percentiles for my item level (Currently 885).
However, the Frost DKs I raid with are not exactly top notch, sitting anywhere from the 30th-60th percentiles.
TL;DR: A rather good Unholy DK several item levels behind can more or less keep up with several much better-geared Frost DKs who are more or less average. Which should mean at similar gearing situations, it becomes a question of skill.