For playing in an organised group with other Templar healers, use:

Breath of Life
Spell Symmetry
Efficient Purge/Purifying Ritual
Blazing Shield
Inner Light

Sturdy Horn/Aggressive Horn/Replenishing Barrier

Multiple Templar healers rotating Breath of Life and Spell Symmetry can keep a group alive forever, as long as healing debuffs are purged.

There's currently a bug with Purge that causes allies to take extra damage from DoT effects, so you may want to consider Purifying Ritual instead: however allies can only synergise the ritual every 15s so it's not a good replacement for Efficient Purge.

Blazing Shield is a great survivability skill if you get focused, or if you're somehow not getting any heals after Spell Symming. If you want you can replace this slot with another support skill such as Blazing Spear or Dark Flare (which, by the way, will completely wreck all those rambo Vampires who think Devouring Swarm makes them invincible).

.....

If you're not playing in an organised group, replace Spell Symmetry with Healing Springs.

Basically what @ThatHappyCat‌ said, Blazing Spear is wunderbar in PvP, helps keeps everyone's stamina topped off. Also great for draining the enemies' stamina if you spam it.

As far as sets go, seducer is nice, warlock is nice, magnus is nice, the undaunted Sphere set is nice, so is the Nerien'eth set. I've also come to terms that vampire templars make the best healers, because they can pop swarm and deal decent AoE damage, and still heal.

Ohhh shoot - now you done gave up trade secrets. You will see my Temp out there now. I hadn't used the Support skills in my build. So Efficient Purge is better than Purifying Ritual, or just preference?
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Never mind that, just read what ThatHappyCat said.