at that lvl and until 83-84 the only difference I found between the 1 buttom spam disc (smite) and 1 button spam holy (heal) was that disc did semi-competent damage meanwhile
Holy is overall more fun, however i would say disc is better if the tank is pulling 1 pack at a time becasue then you can push out some dps, or if the tank pulls 5 packs at time you will still be able to keep everyone up.