The best book I've ever read is perhaps "cheating" because it's "The Next Whole Earth Catalog" and, as the name says, it's a catalog of (mostly) books.

(You can see it for yourself in all it's glory here: https://www.wholeearth.info/p/the-next-whole-earth-catalog-f... )

Other than that I'd have to say the Tao Te Ching.

(The best fiction book I've read is almost certainly "The Book of the New Sun" by Gene Wolfe. It's in the league of Tolkien and Dune.)