The selection of books specifically on Ashtanga Yoga is so large that the following list is definitely not comprehensive:
Sri K. Patthabi Jois: Yoga Mala
R. Sharath Jois: Astanga Yoga Anusthasana
Richard Freeman and Mary Taylor: The Art of Vinyasa
Kino MacGregor: The Power of Ashtanga Yoga
Kino MacGregor: The Power of Ashtanga Yoga II
Gregor Maehle: Ashtanga Yoga – Practice and Philosophy
Gregor Maehle: The Intermediate Series – Mythology, Anatomy and Practice
Lino Miele: Ashtanga Yoga
Linda Munro and Gérard Disse: Ashtanga Yoga – The Primary Series, Yoga Chikitsā
Petri Räisänen: Ashtanga Yoga
Petri Räisänen: nāḍī śodhana – The intermediate series practice manual
John Scott: The definitive step-by-step guide to Dynamic Yoga
David Swenson: Ashtanga Yoga – The Practice Manual
Each book has its individual advantages and disadvantages, one may have a large theoretical background, another almost none, one many pictures, another focussing mainly on the exact sequence.
The classic is certainly Yoga Mala. The other books are also all interesting – I could not objectively chose “the best Ashtanga book”. This is also a question of taste. Personally, I like the two books from Petri most, as he has written them in close exchange consultation with Patthabi Jois and his grandson.