Lesser Heal: This is the first healing spell you get, starting at level 1. Rank 1 heals average 51 for 30 mana, or 1.7 hpm (healed per mana). Rank 3, the final rank, at level 10, heals 146 for 75 mana (1.95 hpm). Out of all Priestly heals, this is the only one no-one ever dreamed of using at max level, because it simply isn't as efficient as later options. For the end-game, therefore, don't worry about it. But for the first ten levels, this is your only option to refill that nice green health bar in a jiffy. Not affected by any talents (except the ones that affect all heals).
Renew: Aside from various set bonuses (8-piece Transcendance and 2-piece Incarnate), this is a priest's only HoT (heal over time) spell. At base it heals 1110 over 15 seconds for 450 mana (2.47 hpm). Of note, it's instant cast, so you can do it while moving or when you don't have a lot of time to spend on one particular target. It receives full benefit from +healing gear, spread over all its ticks. Affected by Improved Renew, which increases the amount healed by the spell by 15% for 3 points, and the Discipline talent Mental Agility, which drops the mana cost of all instant-cast spells by 10% for 5 points, as well as the talents that affect all heals.
These factors conspire to make Renew a very efficient heal in many circumstances. For instance, with healing gear on, my priest gets 7.54 hpm from Renew (talented and with around +1600 healing). Generally recommended to keep on the tank at all times, and also a good "patch" spell for when a rogue takes a cleave or something, since you can just fire it and forget. It's especially efficient as part of a sequence of heals, since you in general want to clump up all your heal casting to stay out of the five-second rule as much as possible. One of my favorite sequences is Greater Heal, Renew, Prayer of Healing on the tank.
Heal: The sequel to Lesser Heal, and prequel to Greater Heal. For a long time it was a staple of the level 60 raiding scene, since once you got enough +healing gear, Heal rank 4 become far more mana-efficient than any rank of Greater Heal, due to its low base mana cost. Essentially, the spell itself was basically just a vehicle for your +healing, which would carry most of the healing burden and of course didn't cost any mana.
However, Blizzard realized at some point that a well-geared priest could cast Heal 4 all day long, and decided to nerf the effect of +healing on spells that were much lower than your current level. Therefore, the spell Heal is rarely used in raiding today. It's your best friend in Deadmines, though. With a 3 second base casting time, it gets 86% of your +healing. Divine Fury reduces its casting time by 0.5 s for 5 points, and Improved Healing lessens its cost by 15% for 3 points. It can also proc Holy Concentration if you have the talent.
Flash Heal: As the name suggests, Flash Heal is a Priest's quickest direct heal (aside from Circle of Healing, if you have it). It only takes 1.5 s to cast, and therefore is pretty good for an emergency. However, there is of course a trade-off for this speed, in the form of efficiency. Flash Heal (also known as fheal or FH) is typically around 70% of the efficiency of Greater Heal, but when you need it, you need it. Its base casting time is 1.5 s, so it receives 43% of your +healing from gear. It is capable of proccing Holy Concentration, and receives benefits from Empowered Healing. Flash Heal 9 gets 4.87 hpm for me.
Greater Heal: This spell makes up the bulk of a level 70 priest's healing, typically. Personally, as gauged by Recap, about 70% of my healing is done by Greater Heal (a.k.a. gheal or GH). This doesn't count Prayer of Mending, however, so the actual percentage is somewhat less. Why do I use it so much? One word: efficiency. That really becomes the watchword for any endgame caster, but healers most of all. Gheal's base 3.0 s cast time means it gets 86% of +healing. The cast time is reduced to a very manageable 2.5 s by Divine Fury (for 5 points), and it works with Improved Healing, Holy Concentration, Inspiration, and Empowered Healing.
For reasons similar to why we used to use Heal 4, I tend to use Greater Heal rank 1 for my "staple" healing, and rank 7 only when it's needed. GH1 tends to hit for around 2000 with my gear and talents, and GH7 for around 4000. Simply put, 4000 is usually overhealing, and GH1 is slightly more efficient anyway, even with a reduction due to its low level. Know it, love it, and stock several ranks: Greater Heal is your friend. Do remember, however, to generally use the biggest GH that is not wasteful, since fewer spells cast minimizes time in the 5SR. Just because two GH1s cost less than one GH7 doesn't mean you should use them if your target is missing 5k health.
The historically-minded might be interested to note that GH wasn't always so popular. Back in the day (before patch 1.10), GH had a 4-second casting time, and there was no talent available to reduce the time. This simply made it too slow for many situations, and Flash Heal had to be used instead, despite its lower efficiency. Fortunately, this is no longer the case, and GH can be used most of the time. 5-man dungeons still favor FH relative to GH more than raids do (due to the fact that there's only one healer typically), but this effect is much smaller than it was pre-BC. GH 7 is 6.95 hpm for me, and GH 1 is 8.81.
Power Word: Shield: This is the first of what I call the "gimmick" heals, which are spells that do something besides straight healing, or do straight healing in an odd way. This particular spell, of course, is not technically a heal at all, but in a group situation it generally functions as once. It absorbs a certain amount of damage, lasting up to 30 s from when it's cast. It's instant cast, and therefore is the only way to instantly keep someone from dying -- or at least it was before Prayer of Mending and Circle of Healing came on the scene, in BC and patch 2.0.1 respectively.
However, it has several problems. It scales horribly, receiving only 20% of +healing (though it used to receive 10%, 20% is still not enough). It is hideously expensive. And at level 70, it typically only absorbs somewhere in the neighborhood of 1500 damage, which is less than a regular hit in many situations. These have led to the spell being rarely used in group situations (though it can be quite handy when soloing).
It is still considered essential to protect AoEing casters that are likely to draw aggro by shielding them, though. This is particularly useful as a shielded caster doesn't lose casting time due to damage that has been absorbed. Pre-shielding Paladin tanks before the pull is also a smart move, since they don't rely on taking damage to generate rage (because they don't use rage), and you can usually regenerate the mana by the time the fight has really begun. Edit: Several paladins in the comments say "don't pre-shield us." Check with your local tank before doing so, I guess. Casting it before combat also causes no threat.
PW:S is affected by Improved PW:S, increasing the amount shielded by 15% for 3 points, Mental Agility, reducing the cost by 10% for 5 points, and Reflective Shield, causing 50% of the damage absorbed to reflect back for 5 points. Even fully talented, though, PW:S is rather inefficient in raids, and I'd recommend avoiding it except for protecting AoEers, pre-shielding Pally tanks, and keeping someone who's about to die alive for another hit or two. 3.03 hpm for me.
Prayer of Healing: Gimmick heal number two. When asked what priests have that make them great healers, players of other healing classes often respond that it is our strong group healing capability. And for once I agree with them. It didn't really seem to come up pre-BC, but in level 70 5-mans, both normal and heroic, Prayer of Healing is really a lifesaver. It's simply an AoE direct heal: it heals everyone in your group within 30 yards for a certain amount. It becomes mana-efficient usually if you heal at least three people with it, and splash damage is everywhere these days.
The cast time is 3.0 s, so it gets 86% 26.7% (being an AoE) of +healing. It's affected by Holy Reach to increase its range, but I don't usually find myself having trouble with that. (I usually stand between the melee and the ranged folks in 5-mans.) Healing Prayers reduces its mana cost, as well as that of Prayer of Mending, by 20% for 2 points. Overall it's the spell to use if you can heal more than two people with it; pretty simple, really. I don't tend to use it much in raids, because the damage doesn't get spread around the right way and I'm usually not in a melee group anyway. 2.1 hpm per target healed for me.
Holy Nova: Technically this spell does cause healing, but it's too expensive to use in almost any critical situation. It causes healing to all friends and damage to all enemies within 10 yards, and makes some pretty lights, but it costs tons of mana. I did use it for healing once when I was in Dire Maul, had a full mana bar, and needed not to draw aggro. (Holy Nova doesn't cause any threat.) Then I promptly specced out of it.
Binding Heal: This spell heals both the caster and their target for an amount roughly equal to a Flash Heal, for somewhat under twice as much mana as Flash Heal. It also causes a lower degree of threat (though this was not made clear until long after the spell was introduced in BC). It has a 1.5 s cast time, and therefore receives 43% of +healing.
With its new lower mana cost, and now that we know it's low-threat, its use becomes apparent: if you're getting beat on, say, or just took a hit, cast a binding heal on the tank. The tank's almost never at full health, and that way you can heal him and patch yourself up at the same time, while hopefully avoiding pulling aggro again. Pretty situational, sure, but useful when the time comes. Can proc Holy Concentration. I get 6.28 hpm off it if both halves of the spell are fully utilized.
Prayer of Mending: My favorite Priest heal. It puts a buff on the target that lasts for 30 seconds and when they take damage, heals them for about the amount of a Flash Heal. Then, it jumps to the lowest-percentage-health target in the same raid (or group) within 20 yards, and hangs out with them for 30 s or until they take damage. PoM will heal up to five times in a single cast. It's ridiculously efficient: even if it only heals one person, it's a pretty good deal; if it procs twice, it's the most efficient spell you have; and if it procs more times than that, it just leaves everything else in the dust. 6.45 hpm per target healed for me.
It's also nice to be able to cast a spell and have it bounce around healing people without you having to do anything. I remember someone once calling PoM a priest's invisible flash-healing pet, and that's certainly what it feels like when it works well. Additionally, the heals from PoM cause threat for whoever they heal, instead of for the caster, so it's a good idea to always have it on the tank before the pull. It's also a 5SR-friendly spell, since it helps you go longer without having to cast anything. Its cost is reduced from its already low amount by Healing Prayers and Mental Agility; if you have both of those (I do) this spell's efficiency is crazy.
Lightwell: Lol. The 31-point Holy talent, Lightwell is one of the most skipped in the game (by "skipped" I refer to the trend that many people, including myself, go past 31 in Holy but don't grab Lightwell). Truth be told, I've never actually used it, so I can't comment in practical terms about its value. What it does is put a well down for three minutes that group members can click to heal themselves for (at top rank) 2361 over 6 seconds. It contains five charges. However, the heal stops if the person being healed takes any damage, so it's basically like a bandage that you can move during. And that's, I think, why a lot of priests don't like to take it -- who wants to spend talent points for a bandage? At any rate, I'm sure it's useful in some situations; maybe priests who like it could highlight those in the comments.
Circle of Healing: Carrying on in Lolwell's tradition, CoH is another top-tier Holy talent that simply isn't very popular. It's a targetable AoE that heals everyone in the same group and within 15 yards of your target for about 500 -- and therein lies its flaws. Basically, it heals for too little to be useful in most circumstances. On top of that, its targeting requirements are too difficult, in my opinion -- in order to be healed, you have to be both in the same group as and within 15 yards of the target. This is not going to heal too many people most of the time. On the other hand, it's instant cast, and I've heard that can make it useful in PvP.
But in its current form, I would rarely if ever use it even if it was a base skill. To make it worth taking over Divine Spirit, it's going to need a raise in power, a drop in cost, and/or a widening of its targeting mechanism. Personally, I would prefer a complete redesign. When the new Priest spells were first announced we had a Circle of Renewal instead, which would place a Renew on everyone it hit, and I was very pleased with that. How about we bring that back?
As with LW, though, I've never actually had CoH, aside from a few minutes toying with it on a test realm. So maybe it's not as bad as I think? Sound off below.
And that's our heals. Yes, we have a lot of them. And surprisingly, a good amount of them are used in end-game situations. In any instance, I typically use Greater Heal, Renew, Prayer of Mending, Prayer of Healing, usually Flash Heal and Power Word: Shield, and sometimes Binding Heal. That's all the non-talented ones. Ultimately, I have to congratulate Blizzard on designing so many different healing spells that are each useful in certain circumstances. As much as I may complain about our efficiency, the difficulty of soloing, or anything else about the class, Priest is still my favorite. (By the way, if you want to check my stats to see what I'm basing my efficiency numbers on, here's my Armory.)