On a one-minute single-boss fight the build is 22/29/0: Discipline as far as 
Mental Strength, for 
Meditation and Intellect, and Holy as far as 
Spiritual Healing.
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0/1005203031305-0350510313000053The search ran separately for every fight and faction. Its results differ only in points our simulator gives nothing, so what follows applies to all of them.
Why these talents
Meditation is the reason to go 20 or more points into Discipline. A healer is casting almost all the time, and Meditation keeps half of your Spirit regeneration running through it. Without it you would heal 2.0 % less. It matters less the shorter the fight: on one minute your mana nearly lasts without it, and it is worth only 2.0 %.
Spiritual Healing adds 10 % to every heal you cast, Renew included, for three points where Classic asked five. It is worth 9.1 %, and about the same on every fight, because it scales the healing rather than the mana.
Improved Healing takes 15 % off the mana cost of Heal and Greater Heal, your two most-cast spells, and is worth 7.9 %. Renew and Prayer of Healing pay full price.
Divine Fury brings Heal and Greater Heal down from 3 seconds to 2.5. On long fights mana runs out before cast time does, so it adds only 4.6 %. On one minute you cast Greater Heal from pull to kill, and a shorter cast is simply another heal. There it is the build's most valuable talent, at 17.2 %.
Spiritual Guidance turns 25 % of your Spirit into healing power, worth 2.6 %. Forever cut its spell damage share to 8 %, where Classic gave 25 % to both.
Mental Strength raises your Intellect by 15 %, a bigger bar and a little more crit. Classic's version raised maximum mana by 10 %. It is worth 0.6 %.
Smaller pieces: 
Holy Specialization (2.3 %), 
Mental Agility (0.0 %) and 
Twin Disciplines (0.0 %). Of your heals, Mental Agility's cost cut and Twin Disciplines' 5 % reach only Renew, the one instant heal you cast.
Improved Renew adds 15 % to that Renew, worth 0.0 %.
Flexible points
About ten points in each build do nothing in our simulator. They pay for the next row: Discipline's third row asks for ten points above it, and Holy's sixth row for 25.
- Silent Resolve and Improved Power Word: Shield open Discipline's third row for Meditation. Neither Holy build shields, so the shield talent scores nothing here. If your raid wants shields from you, it is the better of the two.
- Twilight Focus, Holy Nova, Inspiration and Holy Reach carry Holy down to Spiritual Healing. In game, Twilight Focus keeps your casts from being pushed back when you are hit. Inspiration gives your target up to 25 % more armor for 15 seconds after a critical heal. Our simulator counts neither, because nobody takes damage.
Inner Focus or Improved Mana Burn fill the last Discipline point. Inner Focus makes one spell free every three minutes, a whole Greater Heal or Prayer of Healing. Our simulator presses it at the pull together with Shadowfiend, which spends it, so it scores nothing in the table below. Take Inner Focus, and save it for your most expensive heal.
What the simulator leaves out
Three Holy talents within reach are not modelled, so the talent search never pays for them:
Prayer of Mending is the 31st Holy point and needs 
Spirit of Redemption. For 210 mana, on a 10-second cooldown, it heals its target the next time they take damage, then jumps to another member, up to five heals.
Litany of Light (two points, fifth row) returns up to 20 % of a heal's base cost whenever it differs from your last heal. These rotations switch between two or three heals all fight, so in game it returns a lot of mana.
Binding Heal heals your target and you in one 1.5-second cast.
To fit Spirit of Redemption and Prayer of Mending, go 20/31: move the last Discipline point and the third point of Mental Agility into Holy. On a three-minute single-boss fight that third point is worth 0.1 HPS to the Horde build and 9.0 HPS to the Alliance one.
What each talent is worth
The table removes one talent at a time and simulates the same fights again, so its values overlap and don't sum to your healing. For a single spare point, look at the last-point column.
On every fight
Across the six fights only the empty points move. One-minute builds put one or two of them in 
Holy Reach, and the one-minute party build goes 20/31 with two. Holy Reach only adds range and radius, which our simulator never uses, so those points are free for Spirit of Redemption and Prayer of Mending.