Urthdigger's got your back. His answer is exactly what you should know about the current WHM.

I'll just add one little thing which is : You should pretty much never have to use Medica as well.
With the lilies you are incentivized to use Afflatus Rapture in combination with Assize when the group takes a big hit, and when that's not the case, you would generally use Medica II over Medica. Of course if you already have a Medica II HoT up on your group, and for some reason there's more damage incoming, you might need to pop a little extra Medica to top everyone off, but honestly this pretty much never happens to me.

So in my opinion i would say your go-to AoE heals would be :
- Medica II when your group takes a standard amount of damage (perfect for healing standard room-wide AoEs in dungeon and normal raids)
- Afflatus Rapture + Assize when your group takes a big amount of damage (about 50% of their HP, for example)
- Cure III when everyone is stacked up and preparing for huge group-wide damage (mostly in extreme content) => Couple it with Temperance + Plenary Indulgence and you should be able to get everyone back over 90% HP instantly


Hope this helps !