Wild Growth
Prayer of healing is the best fucking spell out there. Such a contrast to all the smart heals we have nowaday. Also casting divine star with 24 people in front of me and seeing all that green numbers on the ui makes me wanna squeal. As holy I also really enjoy the divine insight ProM proc.
Slightly important to me that my main spell feels good.
Taking into account changes that comes in (Warlords of Draenor);
Druid uses Healing Touch, Monk uses Soothing Mist, Paladin uses Holy Light, Priest uses Greater Heal and Shaman uses Healing Wave.
Out of the ones you use most that I just described, I enjoy Soothing Mist the most because it's a spell you channel.
But out of the others who have casting time, I would say Healing Wave is best because of the beautiful water effect and pleasant sound.
So far I have healed as a druid (Through Heroic Dragon Soul 8/8) and as a priest as an alt. I really love my druid, but I think it's time for a change. Priest next expansion.
Favorite healing spell.... hmmm probably either tranquility or wild growth(brought a lot to the healing toolkit of druids), although rejuvination is amazing. Nothing is better than looking at your raid and seeing 11-12 rejuv's currently ticking on raid members..