Well, they differ depending on your +healing.
For a general idea, just divide the amount of an avarage heal trough the amount of mana a heal costs. The number you get is the heal per mana done, the higher the better.
Using this technique I worked out for myself that Greater Heal (which was sitting at ~5 hpm at 67) is the most mana-efficient. Holy Nova is only effective (read: more effective than Greater Heal) if you heal ánd damage at least 3 targets. Flash heal I recall as being a bit less effective as Greater Heal (~3 hpm), my renew was quite high (~7 hpm) and when I calculated the whole bunch I didn't have PoM yet.