Which method should be used to achieve the most accurate world tracking experience with ARKit?

My company is developing an Augmented Reality app for a client, using ARKit, and they want the best world tracking experience on iOS. We have told them that this is not an exact science and that small variations are perfectly normal, but they want us to do anything possible to minimize errors, drifts and movements from holograms.

We have tested some ARHitTestResult examples on Unity and some others that use ARImageAnchor, but we can't decide on which is the best. It seems that using an Image Anchor improves tracking, but I am not sure if that is really the case or if this is just an optical illusion.

Please advise or share any Unity/Apple documentation on this matter.

Thanks