Chain Heal will be nice. Honestly though HS totem is a bit underwhelming to the point I don't know if I would trust it to keep you topped off when you Lifetap. Honestly you might consider a shadow priest (VT) and the extra shadow damage debuff. Holy Priest with COL would help too. Or even a Druid throwing rejuv and eventually Lifebloom around. There are a lot of ways to go. The synergy between a Shadow Priest and a group of Locks is better. Of course the Pally would benefit from Shaman totems like Wrath of Air and such. Totem of Wraith would be a nice boost to your locks DPS as well. So that being said I would say either a Shadow Priest or Shaman.