Shamans get 3x the slots in 40 mans that druids do. Resto shamans are very dominant in 1.12 content due to chain heal bounces being smart (they auto target low hp people) and very mana efficient. Add on all the utility shamans bring (wf totem, tranquil air totem, mana spring, mana tide, reincarnate) and they are the most in demand horde healer.
Druids on the other hand get the least amount of slots for healers due to their heal over times not stacking which are their best heals. That means that only 1 druid gets to HoT the tank, and their regular heals are the slowest in the game so they get sniped by priests and shaman. Utility wise they are decent, with battle rez (only good when your raid screws up but with 40 people that isn't that rare) and innervate which is decent. The problem is Mana Tide + Mana spring outperforms innervate, and battle rez is only good when people screw up while windfury/tranquil air are always VERY good.
Leveling they are fairly equal, neither is very quick but both die rarely and do respectable damage.
