
master_marshmallow |

Hard pressed to find a superior healer to the Life Oracle, given the sources.
Safe Curing, Combat Healer, and Enhanced Cures make you better at healing than any cleric. You also get more spells thanks to being a spontaneous caster, and the oracle is much more SAD than a cleric ever could be.
Tack on Reach Spell and you're golden.
Otherwise, I recommend the Community Domain on a cleric since it's the only way to get Greater Status, thus removing the need for reach spell.

BretI |

In my opinion, the three most effective methods would be:
Oradin: A Paladin/Life Oracle. Concentrate on Life Link and Lay on Hands. This allows for efficient in-combat healing of wounds but you drop behind a straight life oracle in terms of spell progression.
Cleric: Still the best overall healer. Concentrate on Charisma (for channels) and Wisdom. Selective Channel and Quick Channel for in-combat healing. You have the whole cleric list of options for condition removal, but need to memorize them. Any cleric that channels positive energy can do this, although certain domains are more useful than others.
Life Oracle: Life Link allows you to transfer wounds to yourself, effectively healing others by using your healing abilities on yourself. You need to select the correct condition removal spells. Since all your healing works off Charisma, you can concentrate your attributes quite a bit more.
Be sure you have something else you can do (such as buffing the party) when you aren't healing.

Moonheart |
Basicaly, the main problem with party healing is that there is an insane gap been a low level cleric and a low level... everything else.
A level 1 cleric can easily feature 9 heal action per day, 5 being multi-target heals.
A level 1... let say, druid, barely manage to have 3 heal actions per day, all single targeted.
So... if you run a campaign where fights are rare, like one fight per day at most, you can try to heal with many classes.
But if you run something like Pathfinder introduction campaign, that can put you in front of 7 to 10 fights per day at level 2, your party will get utterly destroyed if you don't have a cleric, simply because you'll run out of healing far before you can rest.
Somwhere in the middle, between those two extremes, you can attempt to make up by buying some wands of cure wounds. It will cripple your party economy, but you will survive long enough for 2nd tiers healer to catch up... and some of those will just perhaps reach a state where they become better than a cleric (like the Oradin)
So... long story short, the main factor is not the book you can pick in, but the campaign you plan to play.