Our secondary stats are the following, please bear in mind that stats can differ per player based on your gear, please sim yourself.
Single Target Priority:
Haste > Crit > Vers >= Mastery > Strength
Mastery > Haste = Crit > Vers > Strength
Critical Strike: Chance for your damaging abilities to deal 200% damage.
Haste: Increases attack speed, reduces the global cooldown, and increases your rune regeneration.
Mastery: Increases the shadow damage you deal through Mastery: Dreadblade. Our pets generally do melee damage and do not benefit much from Mastery.
Versatility: Increases damage dealt, healing done and reduces damage taken.
In general you want to run a Haste and Crit heavy build. For certain encounters, or if you mainly do M+, a Mastery/Haste build makes sense even though Mastery is your worst stat for single target.
The best way to calculate stat priorities for your character is to "sim" your characterFind out how to sim
Troll > Undead > Bloodelf > Orc > Goblin > Tauren
Gnome > Human > Worgen > Night Elf > Draenei > Dwarf
Potion: Battle Potion of Strength
Flask: Flask of the Undertow
Health Potion: Coastal healing Potion