Priest has the most varied and flexible toolkit of the healers in Forever and shines particularly in solo healing content like dungeons where that flexibility is most tested.
Priest can excel in any group composition and while
Priest doesn't bring quite the same utility/group damage punch as Paladin buffs or totems (
Windfury Totem for the melee especially) it provides the highest level of safety with its high healing and does have decent group buffs in
Power Word: Fortitude,
Divine Spirit,
Shadow Protection, and great utility in
Dispel Magic,
Fear Ward,
Mind Soothe (highly underrated for skipping humanoid mobs),
Power Infusion, etc. Prehealing with
Power Word: Shield and leveraging
Renew allows
Priest to efficiently chain pulls and extend drinks/5SR windows. Its ability to dump mana to catch up from behind or get out of a sticky situation is best in role.
Priest also has access to fun 5m specific builds like
Holy Nova +
Searing Light and
Spirit Tap +
Shadow Word: Death (both of which are actually quite strong mathematically). Both Discipline and Holy are strong in dungeons however
Prayer of Mending is a standout in any dungeon that does consistent AOE group damage.
Druid similar to
Priest is rated this highly not because it has the best utility or group damage contribution, but rather because it has a flexible and powerful healing toolkit suited to the 5 man environment. Two extremely powerful hots in
Regrowth and
Rejuvenation allow you to extend healthbars and abuse 5SR to become extremely mana efficient even while chain pulling and
Wild Growth +
Gift of the Earthmother allow you to burst extremely high HPS when things go south. While
Druid is much weaker at focused tank healing with
Healing Touch being relatively weak your HoTs and
Swiftmend should be enough to handle the majority of situations. While
Druid lacks a magic dispel it brings great damage and threat in
Thorns, solid group buffs in
Mark of the Wild and can apply important debuffs like
Faerie Fire and
Insect Swarm if needed at relatively low cost. While
Innervate is often reserved for personal use it can also be a very potent dps cooldown for mana users.
Druid also brings a battle res in
Rebirth and, new in Forever, a normal out of combat res as well. Similar to
Priest
Druid can, at very low cost to its healing, hybridize into Catweaving or multi-dotting with
Insect Swarm to contribute extra damage and can leverage
Omen of Clarity procs to do AOE damage with
Hurricane.
Shaman is in A tier because while it has insane group utility with totems it requires a specific (usually melee heavy) comp to truly shine and can struggle to catch up when behind and sustain its mana as well as the two S tier healers. However in the right comp that fully leverages the power of your totems and with players who are willing to play and position around you a bit more than they might have to with a
Druid or a
Priest
Shaman will look S+ tier.
Chain Healand
Riptide are incredible but have a much lower peak HPS output than
Priest or
Druid so when things go south you can fall behind and cause deaths/wipes. Other than your totems you also bring
Earth Shock which interrupts at range on a 6s cooldown as well as
Ancestral Fortitude for the tank.
Paladin is going in to the Forever launch quite undertuned, and while this will eventually be fixed given that the game is going to be actively balanced, for the time being it might struggle to keep up with healing checks if high level dungeons do enough damage to test the more numerically powerful healers. Holy Paladin also has some design and toolkit issues that hamper its effectiveness in solo healing environments because, similar to
Shaman but to a higher degree,
Paladin struggles to do burst healing as well as sustained high healing. Its best heal in
Flash of Light is very mana efficient but doesn't hit very hard,
Holy Light is a bit more powerful but still underwhelming compared to the core kits of the other three healers, and its new toy in
Light's Vigil is a great pre-pull cast and gives us a novel AOE/burst heal but is simply numerically undertuned compared to things like
Wild Growth and
Prayer of Mending. Paladins saving grace is its incredibly powerful group buffs and it will still be a solid option if you can either pair it with some off-healing or if endgame dungeons don't require much healing.