If you are looking for the best book for USMLE for anatomy you have few options- First Aid for step-1, High Yield Anatomy, USMLE road map to gross anatomy and Kaplan.
First aid is too short for USMLE anatomy. It is better to mix up High Yield with First aid. Some prefer First aid and USMLE road map to study anatomy for USMLE. Kaplan is has all the aspects of anatomy gathered in one book, other than nothing special.
But keep one thing in mind anatomy in USMLE step-1 itself is a low yield topic and many of it is earned through studying other subjects. Again, it is too large to cover all the areas. So my recommendation would be - Do not use too many books and do not give too much time behind anatomy for USMLE.
Another thing, nerve plexuses are a hot topic in anatomy in USMLE step-1.