Best ACT book 2019? Or online course?

Hi~
I’m planning on taking my first ACT on the June 8th date (can’t take April due to the fact I’m traveling) and I’d like to know what’s the best book for self-study. Or should I take an online course like the online ACT course that the official ACT website offers/Princeton act online course? I’m not sure if an online course would work better than a hard copy book. I plan on buying the ACT black book closer to my date so I can work more on test strategies, so as of now i’d like to have a book that focuses more on content. Thanks!

The Official Act Prep Guide 2018-19 is a great book to get started with. I will also add that my daughter used For The Love Of ACT Math and For The Love of ACT science pretty much everyday for 3 months.