pick books by how much the writer had fun

Examples - Linear Algebra Problem Book (book) by Halmos - Problems for Mathematicians, Young and Old (book) by Paul R. Halmos - Crafting Interpreters by Nystrom

Best books are those that the author had fun writing it. Pick books based on that, as it will lead to reading great books. Keep a fun barometer. The amount of enjoyment can be understood when reading a book.

Fun books are those written during inspiration times (i.e. at flow ). Books written on demand (e.g. textbooks) are almost always boring. Translations of most classical books are also written on demand, based on some organization asking a writer to translate it.

A corollary is best books are curations. They are written by gathering and organizing piece of smaller notes/essays written beforehand during inspiration times (e.g. Hackers and Painters (book) by Paul Graham, Zero to One (book) by Peter Thiel, The Anthology of Balaji). Best pieces are either written during flow or they are those curated from smaller pieces that are written during flow. They are more like combinations of blogposts, essays, notes.

An observation. For a lot of books and articles, the writer enjoys it in the beginning, but starts get bored closer to the end. The fun barometer shows higher in the beginning than at the end. An example is Group Theory and The Rubiks Cube article. Its initial parts are awesome. The author wrote with excitement, but she clearly get bored closer to the end. This can be understood when reading it.