Which healer too pick?

I come from MoP and WoD expansions and I thought "hey let's try vanilla" and I found this server. Well I tried to play a druid and I must say you can't faceroll here. Nothing wrong with that though
. Mana seems to be a serious issue here. So I wanted to ask which class is most mana-efficient? I have most experience with pala and druid but I don't know my knowledge is even applicable here.
I hate it when somebody dies (especially in 5 mans), I take that very personally. However in this expansion I can't help a tank who decides to go jackass. I can do a bit extra healing in later expansions but not here. I always try to keep everyone alive so maybe an aoe heal? I really have no idea how healing classes work in vanilla. Can you help me out?

I hate it when somebody dies (especially in 5 mans), I take that very personally. However in this expansion I can't help a tank who decides to go jackass. I can do a bit extra healing in later expansions but not here. I always try to keep everyone alive so maybe an aoe heal? I really have no idea how healing classes work in vanilla. Can you help me out?