Currently, the best covenant for Holy Priest is Kyrian. Unfortunately, none of the four covenant abilities are looking amazing for Holy but Kyrian does offer some value.
Ultimately, your covenant choice will not make a big difference in your throughput for holy, Necrolord and Kyrian are both close in throughput (2-4% of your overall healing), whereas Night Fae and Venthyr do not add any throughput, but may be better for other aspects of the game if you for instance do PVP, playing Discipline or playing Shadow.
The Kyrian covenant ability, Boon of the Ascended offers a 10s window where you have a high single target nuke that heals in Ascended Blast and a decent, spammable ability in Ascended Nova which heals around you for a small amount. After the 10s window, you release a decent sized explosion of healing and damage around you. The spell power value of Blast is high for an instant cast and neither Ascended Blast or Ascended Nova costs any mana, so you have a 10 seconds time window of spending 0 mana.
The Kyrian covenant ability gives you a 3 charge potion that does not share CD with healthstone or healthpot, heals you for 15% of your max hp and removes diseases, poisons, curses and bleeds from you. This can remove some very powerful debuffs in Mythic+ and raid.
Soulbinds and Conduits
Since Kleia’s crit buff was recently nerfed, it is now recommended to pick Pelagos. He offers you a potency conduit and an endurance conduit. On top of this, his key ability: Combat Meditation offers you a large amount of mastery every time you activate your Boon of the Ascended. It has an extra mechanic, where you spawn orbs around you and walking into those extends the mastery buff by 3 seconds per orb. This is a very strong trait for both Mythic+ and raiding, since generally, you will be using your Boon of the Ascended on high damage intake moments, such as the last 10-15 seconds you are fighting the Prideful affix, making mastery very valuable.
Potency: Resonant Words - this potency conduit offers you a very large Heal or Flash Heal after every Holy Word. In both raiding and Mythic+ this conduit will give you a very powerful single-target heal. Using the effect from Resonant Words is most effective on Heal, but do not be afraid to use it on a Flash Heal if you deem it necessary.
Once you unlock a second potency slot, you will likely want Focused Mending, which offers a small healing increase throughout the encounter.
Holy Oration will be better than Focused Mending, but only if it gives you a Holy Word: Salvation that you would not be able to cast otherwise, it is, however, going to be a risk that we do not recommend taking.
Endurance: Translucent Image - Reduces your damage taken for a short duration after pressing Fade. Gives Holy Priest just a slight increase to their survivability, which is much appreciated for a low mobility class without impressive defensives.
Legendaries for raiding
Best legendary: X’anshi, Return of Archbishop Benedictus.
After Spirit of Redemption expires, you will revive at up to 100% health, based on your effectiveness during Spirit of Redemption. After reviving, you cannot benefit from Spirit of Redemption for 10 minutes.
X’anshi was a fan favourite in Legion when it was first introduced, and to the joy of holy priest players, it has returned in Shadowlands - effectively once per encounter, you return to life after dying without consuming a combat res. It is great for progress where mistakes do happen. It is also going to allow you to keep pulls going for longer and allowing your guild to progress faster.
If you’re very confident in the encounter and you can find a good spot, dying on purpose to trigger Spirit of Redemption can allow you to produce a lot of healing with no mana constraints.
Echo of Eonar - Your spells and abilities have a low chance to summon a spiritual familiar to your side. Increasing your healing by 10%. This effect is duplicated on up to 3 allies at 50% effectiveness, preferring allies with the same role.
Despite just being a flat increase to the healing of you and your other healers, Echo of Eonar will overall be the second-best option for you to select, for your raid teams overall healing throughput.
Alternative legendary: Harmonious Apparatus: Circle of Healing reduces the cooldown of Holy Word: Sanctify, Prayer of Mending reduces the cooldown of Holy Word: Serenity, and Holy Fire reduces the cooldown of Holy Word: Chastise by 4 sec.
If you are confident in yourself not dying, and the encounter has no good place to intentionally trigger X’anshi, Harmonious Apparatus will make your Holy Words available slightly faster, allowing you to have a slightly bigger throughput.
Second Alternative: Vault of Heavens Leap of Faith instead causes you to leap to your target, and has 2 charges.- It offers quite a strong off the GCD movement ability, it has a bit of mana cost tied to it, but the movement is surprisingly good. It is unlikely to be better than X’anshi or Harmonious Apparatus, however. When you are using Pelagos as your soulbind, at 25 renown you have the option for a finesse conduit slot, you can select Move with Grace to reduce Leap of Faith cooldown by a good amount.
Legendaries for Mythic+
Twins of the Sun Priestess Power Infusion also grants you 100% of its effects when used on an ally.
In Mythic+, your optimal play is usually giving Power Infusion to a DPS player, generally, this will be on larger packs where Power Infusion boosting you as well will have some benefit. Even during boss fights, as mentioned previously Holy Priest has the ability to do a lot of damage in Shadowlands and this legendary will allow you to help your group with even more damage.