Blossom of Pure Snow
For destruction warlocks? I like to pop dark soul and a trinket when I have 4 embers to maximise my damage from them.
With the blue I do 20,000 more damage on my chaos bolt(when i dont have any buffs) than I do with the epic.
However the epic's cooldown is 1min, so I can dump my embers every minute instead of 2 and a half, and I dont need to let dark soul be ready for 30 seconds while I wait for the 2min 30sec cooldown of the blue.
But, as said, the blue increases my damage of each bolt(without buffs) by 20,000.