Priests - Jack of All Healing Spells
Why you bring them: Efficient big heals (+3k hp), low aggro healing, group heals
Utility: Demagic/Dedisease, HoT, Fort/Imp Spi
Not so good at: Continuous quick heals, surviving a hit, not complaining that they're not "the best healers evah"
Most common misconception: That priests can do everything or that they're a waste of cloth. It's hot or cold with the critics of this class. The first part pertains to priests having the largest number of healing spells available to them: 8 if you don't count the Angel of Death or Lesser Heal. But having and finding the best use of those spells is two different things. Yes, Flash Heal is a fun toy. Will you outlast/heal pallies by using it 24/7? No. Priests are certainly not a waste of space, though. I consider them the work-horses of the raid, handling significant portions of damage with Greater Heals, and you definitely want a couple with you at all times. When you hit MH/BT, you'll also see a step change in utility with CoH.
Always use them on: Tanks, High damage raid healing, low healing aggro situations
Druids - You're HoT!
Why you bring them: Insta-cast HoT's, exploding Lifeblooms, someone has to wear all the leather skirt lewts
Utility: Paw, Swiftmend, Innervate, Battle Rez, Decurse/Depoison, Cyclone (50DKP if you know when you use this in a healing situation!)
Not so good at: Group heals, continuous quick heals, low aggro healing, not jumping during fights
Most common misconception: Druids can't solo heal their way out of a wet paper bag - supplemental healing only! This is slightly true if their target is experiencing highly random and severe damage. If you're looking at a steady beatdown with predictable incoming spike damage, droods iz 4 u. The best example I can think of is using a druid on the 2nd or 3rd Hellfire Channeler tank for Mags so s/he can switch to MT healing once the boss pops. You know when and how much damage is going to happen, so druids can be ready for it. In fact, we've had one manage the 5th Channeler tank with little issue until the 4th dies. But we always used 2 healers on the 5th tank at that point anyways.
Always use them on: Tanks, Raid damage cross-healing
Shamans - <3 Chain Heals
Why bring them: Chain heals, totems
Utility: Group mana/hp regen, AoE Depoison/Dedisease/Defear, Purge, AoE Resists, Group buffs
Not so good at: Continuous single-target quick or big heals, low aggro healing, making friends when they Water Walk people on Lurker
Most common misconception: Shaman are for raid healing and totems only. Yes, they're the win 99% of the time on raid healing, but this can be a serious Achilles Heal (Caution, that was both an awesome pun and there are zero non-nekkid ancient Greek sculptures, even on wiki.). Chain heal only loves those near each other. If the raid is spread out a la Loot Reaver, you want the shamans helping on tanks and melee specifically. Yes, it's a subtle difference between "all" and "not the ranged", but the last 1% of a boss's life is the longest. Don't spend it kicking yourself.
Always use them on: Raid, Tank Rotations, Melee
Paladins - Quick, Fast, and Speedy
Why bring them: Continuous quick heals, can take a hit clear up to limited AoE off-tanking
Utility: Buffs/Debuffs, Depoison/Dedisease/Demagic, BoP, Group Resists, BoFreedom, high-aggro healing, Turn Undead (haha j/k)
Not so good at: Group heals, HoT's, continuous big heals, letting go of the past
Most common misconception: Paladins suck at raid healing. I concede that they struggle with massive amounts of heavy raid damage (i.e. Naj'entus), but anything short of that and you're looking at some lovely 1k-1.8k heals raining down from the skies. It's like a HoT whose ticks concentrate on whomever they're needed the most. And I've done some emergency big heals in my time, should the situation call for it.
Always use them on: Tanks, Specialty Healing, Raid
Of course at this point, you're thinking I'm done and going to wrap things up. Pleheez. Before you all win me the "Most Angry Commenters" award, I have a few notes of my own I want to share. Ok, so they're mostly explanations since not all of my terms are linkable.
Low-Aggro Healing: If at any point the boss your fighting drops aggro on the current tank, you're going to need low aggro healing to keep people alive. Hydross will be the first fight you'll hit like this, but there's many more. Priests are the best at this, using Fade, PoM on the incoming tank, and Binding Heals on the current tank.
High-Aggro Healing: If you have a bunch of adds spawn during a boss fight, the goal is to control their positioning and keep them away from other healers and dps. Murlocs during Morogrim and Elites/Striders on Vashj are good examples. Stick a pally where you want the mobs to convene. Take their Salv and have them put on Righteous Fury. Right when the mobs spawn, the pally will cast a max rank Holy Light. Priests are also able to do this by taking off Salv, but should the real OT be slow, they probably won't survive if Fade is on cooldown.
CoH Priests: Don't start respec'ing to CoH unless you completely fulfill the following requirements:
1) You're working on Vashj and healing the melee in the middle or are in MH/BT
2) You have at least 1 priest available in the raid to provide Imp Spi.
Why? CoH works by group and by range, and for all of the earlier bosses your groups will be set up for optimal buffs (not healing) and you'll be fairly spread out. You also need a significant chunk of +Healing to pull this off (i.e. T5 or equiv). Likewise, you can't skimp on Imp Spi because of the dps race against enrage timers. At the SSC/TK level, you're looking at around +30 dps for mages, as an example.
Now I'm done. Next week I'll surprise and delight you with another topic. And don't forget I'm looking for more nominations for healing strat boss breakdowns. Have a boss that's eating your healing cookies? Lemme know about it (firstname.lastname@example.org) and maybe I can help.
Marcie Knox has been healing lead for over a year, including old school AQ40/BWL/Naxx. She has suffered through holy priest and now basks in the glory that is healadin. Her pally is currently trying to keep Blizz's latest attempt at making cosmic wind chime vampires seem angelic from falling in her eyes. I'm a Blood Knight, darn it! Gimme something that's red and evil looking!