The OnePlus 5 has a 16-megapixel sensor and a 20-megapixel telephoto lens while the Honor 8 Pro uses a 12-megapixel RGB sensor and a 12-megapixel monochrome sensor. The OnePlus 5 primarily uses the second sensor for better portraits by using it to calculate depth. The telephoto lens is only used in the photo mode when zooming into the subject. As for the Honor 8, the monochrome sensor is used to capture better details .Now it depends upon you well i think the winner for back camera i honor 8