I'm in the final polishing stages of a novel and I have two endings that both blow me away and I feel are very, very strong.
Obviously, I can only have one ending. The story doesn't lend itself to a trick where I can write both into the book, but one of them turns out to be a dream and then the real one follows (I remember one or two stories like that). No, with my story and especially my protagonist that wouldn't work.
The problem is that they are opposite endings. One of them is a final turn towards the good, where after everything is lost and all scores settled, the POV MC at least is reunited with his lost love (lost her around the middle of the book, with the loss setting off most of the second part). Strong, happy ending.
The other ending also has him find her, but this time she reveals that those he hunted down and eliminated were actually her allies and she stayed hidden throughout the 2nd part of the book by her own choice because she wants to be as far away from him as possible. Fade to black, closing off all the loss and destruction with the only personal loss that actually matters to the MC. Strong, dark ending.
And I keep reading and re-reading them. I've settled on the dark ending for now, but the scales are pretty balanced and a tiny swing in mood could convince me that the happy ending is the better one. Both endings provide closure and finish the story so nothing else can be said. Both bring all character arcs and storylines to an end. Both provide closure for the reader. Both leave me personally satisfied, just in completely different ways.
I have a low number of test readers, so not a statistically significant sample to question.
Is there a tested and proven way to decide which ending to choose?