The obvious choice would be Mark of Protection used on a target being hit by a fiend army - with enough fiends it could be healing for several hundred hp per second. Same kind of thing goes for healing seed, but actually this would take first place if you took into account multiplying that huge figure per second by the 7 other people who could be standing near enough to get the effect.
As for others, though. I think perhaps second place could go to Restore Conditions? There are, what, 7 conditions a person could be under, and at 70-odd heal per condition removed that adds up to 500+ heal. (btw, i love being a prot with this skill - modded iway with trappers and tainted i just see as an opportunity

What else is there? Healing spring could be good with people balled around it. Heal party isn't bad. Any thoughts?