I main whm and i lvled all 3 healers and I personally play Whm and Astro I really don't like to play sch. If you mean by involment it depends on the player. Learn to stance dance. In my opion sch might be a bit to easy with stance dancing as fairy picks up the slack when u not Healing so is a bit more forgiving. Why mage is next on the line as all u have to do is spam your HoTs on the target or raid and dps away. Astro may be what u looking for as there is a lot of going on with the cards, dps, and healing. So timming everything may be the challenge that u looking.