What is the most authentic and best book on Sri Aurobindo’s biography🙂?

There are quite a few, as given below. 

1. Sri Aurobindo or the Adventure of Consciousness by Satprem.

2. The Life of Sri Aurobindo by A B Purani.

3. Sri Aurobindo, His Life Unique by Rishabhchand 

4. Sri Aurobindo by K R Srinivasa Iyengar.

All these are good and authentic. The choice of the best depends upon individual preference.

Affectionately

Alok da 

Reference: 

त्याग ओर सन्यास | MY 013

YT Link: https://youtu.be/ZbQQXh2np2o