Highest Damage Relics

[Disenchantment]

This is from highest to lowest.

Mind Shattering (5% Mind Blast damage)
Unleash the Shadows (15% chance of Shadowy Apparitions from Vampiric Touch)
To the Pain (6% Shadow Word: Pain damage)
Touch of Darkness (5% Vampiric Touch damage)
Death's Embrace (3% Shadow Word: Death damage)
Creeping Shadows (1% Shadow damage)
Void Corruption (5% Mind Sear damage)

[Disenchantment]

Also as a side note, maybe more for PvP purposes, this is better for surviving.

From the Shadows (-10sec Dispersion cooldown)
Thoughts of Insanity (10% Shadow Mend healing)
Touch of Darkness (5% Vampiric Touch damage)