Thank you very much!
The best book is the red one put out by the ACT company itself. Get the newer edition, it has more practice tests.
The Meltzer ‘For the love of’ series is supposedly very good. I have read a lot of posts where people praise various books in it.
I have also read praise of the CollegePanda books.
We got the ‘Up Your Score ACT’ book and it worked well for my particular kid. The colloquial writing style is occasionally annoying but it was a good read and kept his interest, and it did seem to reduce his anxiety over the test. It may work for you, it may not.