Lord,
The shammy is the best to duo with any class because even tho a shaman is not the best at anything but standard buffs and slows(75% slow at max) they are not the worst at anything, so for an all around utility, healer, dot dmg, nuke dmg, pet dmg class...shaman is the easiest answer. yes a bard can slow and haste, but if those things are already taken care of there are better songs to be playing.