I had the same healing comp as you, and I would definitely say Holy. You have a pretty strong tank healer with an Hpally. I chose using Solace over Mindbinder due to some downtime, to help DPS, and the fact that mana usage varied throughout the fight, so I preferred my Shadowfiend.
Ellumina did you end the fight with any mana or where you completely oom at the end? You are casting 91 solaces in 9:20. In that time you can cast 10 mindbenders each giving you 5.3% of max mana over the shadowfiend. 91 solaces are 91*0.7 = 63.7% of your max mana. The difference is 30k mana.
Also are you casting a lot of solace outside transitions, when there is healing to be done.
We had 4 attempts on him yesterday. I think discipline is ok too, but its extremely complicated. You have to have 5 evangelism stacks ready. You have to heal quite inefficiently by spamming aegis on two groups then you need to time cast spirit shell on three groups only. You need to time it shell perfectly so that you have 2 casts remaining when the add starts pulsing. Finish the two casts pop archangel cascade about 2s before he overloads and then PoH all the way until AA ends. Then stack AA again keeping all left over aegis alive and on the next add pop it 10s before it starts to pulse and go to town on all the groups.
It is really complicated to keep everything up. When you squeeze about >2m healing from the damage of each protector.
A less complicated version is to stack archangel pop spirit shell a few seconds before the protector spawns and then spam it on three groups (two PoHs on each group), then as soon as spirit shell ends pop archangel and PoH/PWS as much as you can before the add overloads, using cascade as soon as the add starts casting overload. The next add is the same as before. You will get less aegis this way, but this is much less vulnerable to mistiming.