Nightblade is almost the best Stamina Healer as Arcanist and Warden thanks to the best Ultimate generate. There is nothing you can‘t do which Magicka Healer can. We use the same sets, but the play style is different as we use martial weapons for healing (Bow and/or Greatsword) and de-buffs (DW and 1H&S).
It's the only Class on which you want the highest possible Critical Chance because of
Nocturnal Inspiration Class Mastery. That combined with
Share the Spoils and Minor Heroism from
Torchbearer generate Ultimate like crazy.
Smash provides Damage Shield, HoT and Minor Berserk – basically our Combat Prayer. Torchbearer also provides purge.
Refreshing Path is going to boost a lot damage output from Banner like something 1.2k+ WSD.
Vault is the out of jail card from large AoE and to heal allies inside it. Cast
Siphoning Attacks every 4 sec if you can, and this is "cheat" skill for insane sustain. Cast
Relentless Focus always if you can kill enemy to gain 10 Ultimate.
Monster sets:
Ozezan the Inferno,
Symphony of Blades and
Nazaray are all good depending on situation.
Sentinel of Rkugamz is the best for beginner.
If Major Courage is covered by Warewolf which is often the case since U50 or if there is other Healer with SPC set, the best alternative set is
Pillager's Profit because of insane Ultimate generation.
Alternative body sets:
War Machine is the best for boss encounters, and for trash, too if you can quickly build up Ultimate, and you should with the proper rotation. If you can't, just use
Powerful Assault as the best alternative.
Apocryphal Inspiration can be used in normal PUG or guild progression trials only if group needs sustain otherwise it's not worth it. Unfortunately Stamina Healer/Support set
Phoenix Moth Theurge is useless in PvE as it triggers on healing and not overhealing plus Minor Force is useless, too as it's easily sourced by DDs. If ZOS one day changes to triggers on overhealing and to provide Minor Berserk instead Minor Force, or replace both Minor buffs with Major Courage, it would become the Stamina version of Spell Power Cure.