What is the best human anatomy and physiology book?

This is contentious. There are several.

Gray's anatomy is wonderful for most of the gross anatomy in situ. However there are a few supplemental books which give more oversight to certain portions of the anotomy.

Illustrated Essentials of Musculoskeletal by Kay W. Sieg is great for muscles and bones as it details origin, insertion, and movements of muscles and it is cheap.

The Guyton and Hall or Mcgraw-hill physiology books are decent enough for their content.