Dear Priyalini, it depends mostly on the purpose of the book. If you are preparing for exams, Chaurasia is the best because it gives point wise information which is easy to read and understand. Given the pressure of reading a tough subject and on top of that remembering all the nerves, their  courses, etc Chaurasia is better. But having said that Gray's Anatomy cannot be brushed aside. It has in depth information and most of medical aspirants use it for reference purposes. But because Physiotherapy doesn't use Anatomy for clinical and research purposes in its treatment, Chaurasia is good. But if you are planing on studying Masters abroad, Gray's is the best.