Hmmm.... so far I have equal view on both paths. A bit of a lore & English noob here, but I'll try to say what I think.
Spirit path will make him true to himself yes, his purpose of helping people and his purity as a spirit of compassion. Letting go of the real Cole seems the best way for him to focus on helping people... in Asunder, I may be wrong, but he doesn't know he was a spirit, hence why he wanted to become "real" and after knowing his true nature, it's best for him to stay that way.
This, is my opinion on the spirit path : he would be pure, and continue helping then make people forget, and that is what irks me. Personally I don't like it if a character stays "perfect" and "untainted", I like it when he goes human and experience all the flaws and negativity.
Human path.... this is a big leap of faith, I believe spirits can do many unique and extraordinary things, and personally I think this spirit of Compassion can become fully human--have the ability to. I agree that being human is not the "perfect" story for everything, but it's the flaw and hardship / hard path he took that makes him more special to me. I headcanon'd that if his main purpose was to help the real Cole... if there's any hope that the mage!Cole's dream can be fulfilled, it's to become like the current Cole--free and without magic. I imagined that the real Cole would be happy to see him "live" on like what he always wanted to be....
I trust Cole enough that he's become human, and negative emotions will not turn him into a demon. Also, something like this line of his : "Now I understand why some things I said to Cullen makes him uncomfortable," this I think will make him understand how to help more efficiently, because if he understands what the people feel and have experienced those feelings himself, he would know how to help without making them feel uncomfortable. Without being too intrusive.
Also when he says that people knew him now--that people know someone cared and wanted to help them, it could make them feel better too. All the memories of the real Cole and his backstory on Asunder caused him great pain, yes, but now he can feel what's it's like being healed himself. I would love for him to meet Rhys & Evangeline again in the future... it would bring me tears.
In tears right now.... T__T sorry he's just so special to me. He's such a beautiful character... /hugs him tightly T__T