This tier list includes the upcoming anticipated balance changes going live on January 10th, based on a review of the top ladders and my personal experience playing. (Adjusted due to agreeing with some posts below.)
S+ Tier:
#1 Restoration Druid
S Tier:
#2 Preservation Evoker
A Tier:
#3 None
B Tier:
#4 Restoration Shaman
C Tier:
#5-6 Discipline Priest
#5-6 Mistweaver Monk
D Tier:
#7 Holy Paladin
#8 Holy Priest
Do you agree or disagree, why or why not? What is your opinion?
RSHAM is def in the top 3. I would say RDruid will 100 % surpass Preservation by the end of the season because it’s constant hot healing. RSham is very strong into evoker / druid because of purge.
Technically I do have it 3rd from the top, I’m just implying the top 2 are significantly better 
I don’t have experience playing other healers, but I definitely feel bottom of the barrel. I feel tunneled to death by melee, and/or CC’d to oblivion while my meager attempts at throwing out instant heals hardly feel worth the GCD.
Meanwhile, if the opposing healer is a PrEvoker, DPS treat it like they’re allergic to it and focus anything else (understandably).
R sham is easily A tier by itself, but because it hard counters the two specs ABOVE it in power, I’d argue that makes it A+ or S- at the very least.