The druid is nice because of the incombat ability to shift into stag form and then instantly IWT to it. With a shaman or other toon having a 2+ person mount you have to wait for them to drop the "in combat" flag that can take 2-3-5-10-or more seconds. Druids do give you a battle rez and if you are rolling enhancement or elemental you can go guardian for some bleeds and easy facing or boomkin for more ranged. Boomkin is nice due to being able to draw eveyone into one area and then AOE silence, pop ascendance on the shaman and then blow them up enmass.