Intellect >>> Haste > Mastery = Crit > Versatility
Haste is more important with wilfreds than other legendaries but there are no realistic caps before diminishing return sets in at 30% haste.
Haste increases your spell casting speed for you and your pets.
Mastery increases your demons' damage (Implosion gets increased by mastery).
Crit Increases your chance to do double damage.
Versatility increases your overall damage and healing and gives you damage reduction.
The best way to calculate stat priorities for your character is to "sim" your characterFind out how to sim
Orc > Troll > Goblin > Blood Elf > Nightborne > Undead > Vulpera
Mechagnome > Human > Dark Iron Dwarf > Gnome > Dwarf > Worgen > Void Elf
Orc and Mechagnome are the only two races that are even remotely far enough ahead of the others to be worth talking about with 0,7% and 0,72% dmg increase respectively.
Intellect: Leviathan's Eye of Intellect
Haste: Quick Jewel Cluster
Food: Tenebrous Crown Roast Aspic (Haste)
Flask: Spectral Flask of Power (Intellect)
Potion: Potion of Spectral Intellect
Oil: Shadowcore Oil (Damage Oil)
Health Potion: Spiritual Healing Potion