I've heard they are still running a lot of the numbers and balancing is still to come but how is the healing working out? I'm more of the pure healer type but do more groups than raids honestly. I think I may actually pick this up after all.
I usually tank for the guild and heal in every other occasions, be it pickups, LFR, dungeons, etc.
This time around I'm not going to tank if I can find some decent ones to group with, but will focus on healing and for my tests on the PTR and the beta readings I did, the main choice you have to do is based on what you like to provide to the group / raid. If you want lots of utilities and cooldowns, shaman and paladin offer the best ones, shaman seems slightly ahead because Spirit Link Totem is simply amazing (and you still have Bloodlust, which in 5 men is not always available). I like a lot the shaman mastery and I'm not too fond of the new paladin one, plus the shammy AE healing is more enjoyable to me, but paladin has a lot of instant casts now, which makes it a lot more mobile than it was in WoD.
Druid is the same as it was, except it has a new mastery that jojo'ed up and down during beta: the more hots a target has, the larger heals it receives, then it was capped at 3 hots, then fuck knows what they did. It went from great to meh, to decent and now I have no idea where it sits in the stat priority, what I know is that druid healing style is very similar to the past, plus it gets Tranquillity on a 2 minutes cooldown and castable while moving once unlocked on the artifact.
Discipline Priest has changed a lot, damage to heal and a more hybrid role is the idea, I honestly still have to try it, while Holy is similar to the past with very large heals on a 1 minute cooldown that can be significantly shortened through the use of other spells. I kinda liked Holy for the few dungeons I ran with it on the PTR, but maybe it could become a bit boring over time, not sure, it's just an impression.
Mistweaver monk is a totally different class from its previous incarnations. I loved it in MoP, considered it decent in WoD (didn't like stances) and I find it pretty boring in Legion.