Inspired by Dawn over on WOW Insider, here are my thoughts on meta gems for priest healers, very quickly (and leaving out the gems that are clearly not healing gems):
- Beaming Earthsiege: Maybe. Gives about 0.45% crit chance and +2% mana. The extra mana will vary depending on your current mana pool; the crit chance means that if you’re Disc, you’ll get another Divine Aegis for every 217 spells you cast, or 1-2 more per fight.
- Bracing Earthsiege: No. Gives 25 spell power and 2% reduced threat. Only take this one if you’re having trouble on the threat meters, which hopefully you aren’t.
- Chaotic Skyflare: No. Gives about 0.45% crit chance and 3% increased critical damage. That’s important. It’s tempting to think “oh, they mean “critical spell effect”. They don’t. It’s just damage. Steer clear.
- Destructive Skyflare: No. Gives bout 0.55% crit chance and 1% chance that offensive spells that target you will hit their caster instead. This is a PVP gem, although it can be useful for certain fights (those involving randomly-targeted spellcasts or poison affliction, for example). Spell reflect does not affect AOE spells, although it can redirect chained spells (like Chain Lightning).
- Effulgent Skyflare: No. Gives 320 health and reduces spell damage taken by 2%. Another PVP gem; if you’re really having that much trouble staying alive against PVE spellcasters, swap out one of your other gems for Solid Majestic Zircons.
- Ember Skyflare: Yes. Gives 25 spell power and 2% Intellect. This gem will directly increase your throughput, and while 2% Intellect doesn’t grant quite as much mana as 2% mana (Beaming Earthsiege gives about 72 more mana regardless of how much Intellect you have), it grants more crit and more regen.
- Enigmatic Skyflare, Forlorn Skyflare, and Impassive Skyflare: No. These give about 0.45% crit chance and various duration-reducing effects. They’re PVP gems with highly-situational PVE uses. Steer clear of them.
- Insightful Earthsiege: Yes. Gives 21 Intellect (about 315 mana, 0.125% crit chance, and mana regeneration that varies based on your Spirit), and every spell you cast has a 5% chance to restore 600 mana. That works out to an average of about 60 mp5 (which can go down if you insist on casting long-cast-time spells and up if you have lots of haste, as I do). This is the beloved, overwhelmingly-recommended meta gem for priest healers; over a 6-minute fight that adds up to 4,320 extra mana in your pool. Get this unless you can afford to be more concerned with throughput than mana.
- Powerful Earthsiege: No. Another PVP gem, this one gives 320 health and reduced stun duration. Not worth it.
- Revitalizing Skyflare: Yes. Gives 11 MP5 and 3% increased critical healing effect. That’s not healing chance; instead, when your heals do crit, they heal for 3% more. That means that if you’re Disc, your Divine Aegis will be 3% bigger too! The 11 MP5 is 792 mana – not fabulous, one additional spell over the course of a 6-minute fight, but it’s better than nothing.
- Tireless Skyflare: Maybe. This is another PVP gem, with 25 spell power and a minor run speed increase, but I ran with it for a long time. Part of this was because it helped me get out of the fire faster, and part of it was because I was entertained by running faster than anyone else in the raid. Sadly, it doesn’t stack with other speed-increasing effects. Go with this if you can’t get one of the others, or if you have a hard time staying out of the stuff on the floor.
- Trenchant Earthsiege: Maybe. Gives 25 spell power and reduces stun duration by 10%. It’s a PVP gem, but it has some uses in PVE. It’s not fabulous, but it can be useful for certain fights, especially in heroics. The faster you can get out of a stun effect, the faster you can start healing again. That said, if you have the chance to get another one of the gems, take it.
The bottom line: Get Ember Skyflare, Insightful Earthsiege, or Revitalizing Skyflare depending on your playstyle, with the first two recommended more highly than the third unless you really, really love Divine Aegis. Get Beaming Earthsiege, Tireless Skyflare, or Trenchant Earthsiege only if you can’t get one of the first three.