Holy paladins can't do it all. While we might be the best-dressed spec in the game, we occasionally need for other healers to give us a hand. The developers have done a great job giving each healer a niche for them to fill. A holy paladin must know the strengths and weaknesses of the other healing classes in order to be able to work alongside them.
While all healers are somewhat normalized by Cataclysm's introduction of the three heal model, it's each class's unique spells that give them flavor. We all start with the same base, and then our signature heals and cooldowns allow us to differentiate ourselves. Holy paladins can adjust their healing style and strategy to complement their partner healers instead of competing with them.
Discipline Priests: Protecting their targets
Discipline priests, our first study, are the masters of preventive healing. While our own Illuminated Healing mastery allows us to put absorption bubbles on our healing targets, we are actually stealing the mechanic from discipline's Divine Aegis. Divine Aegis' potency far outshines our own Illuminated Healing, allowing discipline priests to raise the survivability of their targets significantly. The downside to absorption bubbles is that they're wasted if they go unused, which makes discipline priests great for handling burst damage but poor for handling DOTs and protracted damage.
Due to their absorption-based healing and their powerful Penance spell, discipline priests make great tank healers. Disc priests also have access to Pain Suppression, one of the best damage reduction cooldowns in the game. Between Hand of Sacrifice and Pain Suppression, a disc priest/holy paladin can cut a tank's incoming damage for 20 seconds. Our combination of powerful single-target healing and damage-reducing cooldowns can keep a tank alive through just about anything.
A disc priest's biggest weakness is AOE healing. Disc's Power Word: Barrier allows them to prevent a lot of incoming AOE damage, but it doesn't actually heal anyone, which means we'll need to use Holy Radiance to assist with raid healing. While I've seen disc priests negate a huge chunk of an AOE attack's damage via Power Word: Shield spam, it's going to fall to us to top everyone off. Beacon of Light allows holy paladins to be excellent spot healers, and so we'll be healing the raid while the disc priest keeps the tank stable.
If there's going to be lots of AOE damage, discipline priests will have us stacking up underneath their Power Word: Barrier. If they're using the Glyph of Power Word: Barrier, then we should to try to dole out as much healing as possible during the Barrier's duration to maximize our healing done. A PW:B and Holy Radiance combination is incredibly effective at handling any sort of AOE burst. We can clean up any remaining wounded players with our cheap heals like Holy Shock and Word of Glory, as disc priests aren't specialized spot healers.
Holy Priests: AOE machines
Holy priests are the antonyms of their discipline brethren. The holy tree specializes in AOE healing and HOTs, with almost no preventive healing or tank healing capacity to speak of. All of holy's signature spells revolve around raid healing. Holy Word: Sanctuary and Renew allow a holy priest to apply powerful HOTs to their targets, while Circle of Healing and Prayer of Healing are amazing at quickly getting a raid group back to full life. Lightwell is an amazing raid heal when used properly, as it only costs the priest a single cast yet can heal over a dozen targets. Prayer of Mending is a smart heal that hops from target to target, healing with each bounce. Even a holy priest's regular heals apply a HOT effect via their mastery bonus.
With their powerful AOE healing and HOTs, holy priests are a great ally to the holy paladin. Our Holy Radiance is quite potent, but it's only effective if our group can stack up, and we can only have it active 50% of the time. When paired with a holy priest, you'll typically be focusing on the tank while they'll be handling most of the raid healing. We can always sneak in some spot healing via Holy Light or one of our instant-cast heals to help out, but it will fall on us to keep the tanks alive.
Holy priests themselves aren't great tank healers, but they can save a tank's life with Guardian Spirit. While Guardian Spirit is active, the tank will receive 40% more healing, which is a huge bonus for our large heals. In addition, if the tank receives a blow that would've killed him during Guardian Spirit, he instantly regains 50% of his maximum life and doesn't die. Guardian Spirit is an incredibly potent tank cooldown, so you'll want to coordinate with the holy priests in your raid to time them properly.
Prayer of Healing is a rather unique heal, as it will only heal players in the party of the targeted player. In a 10-man raid, for example, Prayer of Healing will only heal group 1 or group 2, depending on who the target of the spell is. You can work with the priests in your raid to assign groups for AOE healing, as this allows the priest to focus their Prayer of Healing onto one party while you use your direct heals to top off the other group. Prayer of Healing is the only spell that I know of that has a party-based restriction, but a bit of communication ahead of time will have everyone prepared.
A tale of two hymns
Holy and discipline priests have access to two powerful hymn spells, Hymn of Hope and Divine Hymn. Both hymns are channeled spells that require the priest to stand still for the duration, so be sure to adjust your healing strategy while they're incapacitated by the hymn. Hymn of Hope is a mana restoration hymn, and it also increases our maximum mana while active. You can use Divine Plea during the Hymn of Hope for some bonus mana, since DP is based on your maximum mana. Be careful though, as you'll only be healing at 50% capacity while your priest won't be healing at all, so save this technique for only the safest moments in an encounter.
The Light and How to Swing It: Holy helps holy paladins become the powerful healers we're destined to be. Find out just how masterful mastery healing can be, gear up with the latest gear, and learn how to PVP as a holy paladin.