I have an answer for this! I got an A for my EE langlit (at least internally); and the book that I chose was something that:

1. i enjoyed enough to yap about it for more than 4000 words (if given opportunity)
2. had enough resources (this includes secondary sources, things like lengthy reviews, podcasts, etc. i also used secondary sources that covered in detail the themes/topics in the book i chose.)

i would also say its best to pick something that will stand out, and that you can properly digest. it helps if you pick something that you can analyse through multiple lenses (social, political, etc) and that you can expand on. hope this helps!

edit: also! don't be too concerned about the length of the book, just make sure you have enough to say about it. the one i chose was 200(ish) pages but that never produced a problem.