Stat Priorities
Item level or Intellect value should not be understated, especially early in an expansion. Very often, if it's a significant item level upgrade (13+ item level) then it will be a DPS upgrade to wear it regardless of the stats. As always, sim yourself with Raidbots.com for an accurate assessment of what gear to put on.
Demonbolt Builds (Sacrificed Souls + Fel Covenant talented):
Intellect > Haste > Crit = Vers > Mastery
Non-Demonbolt builds:
Intellect > Mastery > Haste > Crit > Vers
Stat Outline
Intellect is just a flat damage increase to all your abilities.
Ultimately it just comes down to damage per point, but here is an outline of what the stats do and how they interact with Demonology’s toolkit.
Haste: Increases casting/attack speed for both you and your pets. This is especially relevant for imps as they have a set amount of firebolts (6) and will time out faster with more haste. To offset this, you summon imps faster with more haste so it evens itself out in terms of rotational gameplay.
Mastery: Mastery increases all of your pets damage as well as implosion and Bilescourge Bombers (if talented). With the amount of pet damage demonology currently has at its disposal this is a very powerful stat that should be prioritized if possible.
Versatility: Gives damage to all your abilities, and half of that damage bonus as damage reduction. In some situations you can choose to use a higher versatility gear setup to survive certain mechanics, although I doubt with the current state of warlock defensives, that this will be an issue outside of PvP.
Critical Strike: Crit does not interact with Demolology’s toolkit in any meaningful way and is just a chance to deal double damage. It is a more sought after stat for Demonbolt focused talent setups as the spell doesn't benefit from mastery.
The best way to calculate stat priorities for your character is to "sim" your character
Find out how to simRaces
Horde
Orc Stands out as the clear winner on the Horde side. Blood fury is a strong main stat buff, and 1% pet damage comes in handy for demonology. Troll looks like the second strongest race as the 3 minute cooldown Berserk lines up very well with Nether Portal talent setups.
Alliance
Dark Iron Dwarf is the best Alliance race for the same reason as orc for horde. Main stat on use is a strong effect to pair with cooldowns. Gnome comes in second place with a 1% passive haste racial.
Enchants
Weapon: Sophic Devotion
Chest: Waking Stats
Legs: Frozen Spellthread
Bracers: Devotion of Avoidance / Devotion of Speed
Cloak: Graceful Avoidance / Homebound Speed
Boots: Plainsrunner’s Breeze
Rings: Devotion of Haste
Gems
Intellect/Haste: Fierce Illimited Diamond (1)
Haste/Mastery: Keen Ysemerald
Consumables
Food: Sizzling Seafood Medley or Grand Banquet of the Kalu’ak
Potion: Elemental Potion of Ultimate Power
Augment Rune: Draconic Augment Rune
Weapon Rune: Howling Rune
Healthpot: Refreshing Healing Potion
Additional Consumables: Pepsi Max for 5% DPS gain!
Phials (Flasks): Iced Phial of Corrupting Rage got buffed with 10.1 and now requires 400% of max hp to be taken in order to trigger the negative effect, greatly increasing its uptime. It is very likely that this flask will end up being the best choice. Phial of Elemental Chaos is a safe choice, but Phial of tepid versatility is not a poor choice and offers a small damage reduction as well.