If your healers are geared enough, you should use it on a Shadow Priest, Fire Mage or Moonkin, otherwise a Resto Druid or Holy Priest are decent choices. If you don’t have the choice, use it on any class that has any kinda dots, just make sure you have that precious 3%(9%) has...
Resto shaman should primarily use + healing gems in sockets, often ignoring socket bonuses. Gems with spell haste can be another viable option. Blue gems should be used sparingly. RED:[Teardrop Living Ruby]or[Teardrop Crimson Spinel]