I've played all the healers apart from Druid and I can easily say that Paladin is the easiest one to play. I currently main a disc Priest and I raid alt raids on my holy Paladin. Paladin is a whole lot of fun as well. With "raid healing" I assume you mean just healing in a raid and not neccessarily the role of raid healing instead of tank healing.
i play a shaman and i must say its very easy, just keep Earth shield on a tank, do riptide and unleash elements on cd.
you have healing wave for normal healing, greater healing wave for when the tank is in danger and healing surge for when u need a fast and big heal.
using riptide will make your 2 next heals faster.
that's all there is to it.