With the avent of book 4 the tension is rising, and we are feverishly awaiting Book 5.
(In my opinion likely due for the month that is the namesake of our heroin from TLJ.)
Naturally one finds the latest book the best, full of action and novelty.
However after thinking and considering the whole story up to this point it might appear that one of the other chapters is really key, and more important
Personally I hesitate between Book 2, and Book 3 (I voted Book 3, but might change it later).
I'll be very interested to have your opinion.