I have read several but I like "The Maverick War: Chennault and the Flying Tigers" by Duane P. Schultz. It gives a background of Chennault before the AVG as well as AVG action. He also wrote a book about Wake Island.
Dan Ford's book "Flying Tigers" is the best overall history of the AVG. There are several excellent first-hand accounts by AVG members including those by Erik Schilling and Charlie Bond.
Little known but excellent reading is "Damned to Glory" by Robert L. Scott and his
more well known "God is my Co-Pilot".
Also the obscure but interesting "Chennault of China" and I can't remember the author's name
but it was written in the late '40's and it was not by Scott.
Dan Ford's history of the AVG is far & away the best. Nothing else compares. Ford researched every source and covers the Japanese side. Almost all claims vs. losses are reconciled.
Two memoirs by AVG pilots, Charlie Bond's A Flying Tiger's Diary and R.T. Smith's Tale of a Tiger, are both excellent.
Dan Ford also has an extensive website devoted to the AVG, "Annals of the Flying Tigers".