It changes with my age and what I am reading at the time.
When I was a little guy, my favourite book was the Little Red Hen, ( something like that ), honing my imagination.
Then it was the Hardy Boys series of books, with their excellence in solving mysteries.
When I read war and Peace, that one was excellent.
Frankenstein by Mary Shelley. Such a terrific story, and a very early science fiction from 1818. I read on Wikipedia that "Brian Aldiss has argued that it should be considered the first true science fiction story."
The Strange Case of Dr Jekyll and Mr Hyde by Robert Louis Stevenson. Another great story, and also an early science fiction from 1886.
Dune by Frank Herbert. Simply excellent. Also SF.
The Picture of Dorian Gray by Oscar Wilde (1890). Also a great story.
Ursula Leguins rendition of the Tao Te Ching is truly excellent. I‘ve read several ones and favor hers over all the others except the Gia-Fu Fung version famous for its black and white photos by Jane English.
Be aware that she rendered it from an English translation into better prose and as such may have altered the meaning of some passages subtly, something a translator would likely be aware of and more careful to translate.
I tend to read mostly novels rather than science or other non-fiction.
The Temple of my Familiar by Alice Walker is my all time favourite. Immense in its scope, mixing the stories of different people from different times and places
In recent years Distantas formas de ver el agua by Julio Llamazares is superb - tells the story of a family returning to the place of origin of the father/grandfather to scatter his ashes. He, as a young man, was displaced when the village was flooded to create a reservoir, one of the big projects of the Franco years. Each chapter is the reflections of a different member of the family, the wife, the children and the grandchildren of the deceased. It's sad and beuatiful and I cried at the end. Sadly it's not available in English but I 100% recommend it for anyone who can read spanish.
I spent 12 years in school in tennessee learning essentially nothing, having known how to read upon entering, (except maybe that f(r) = 0 iff (X-r) divides f(X)). Then in college, i encountered a footnote on page 27 of Calculus and analytic geometry, by richard courant, that derived the entire sequence of formulas for the sum of the first n, rth powers: 1^r + 2^r + 3^r +....+n^r, for every r and every n. I knew i wasn't in kansas, or rather tennessee, any more, toto.
@mathwonk after encountering Courant, I should think it was time for "lions and tigers and bears, oh my."
For me being a physics major dabbling in math, it was Algebraic Topology before I had Set theory, Groups and Rings and how to prove the theorems. The prof was kind though but the math was beyond abstract for me. I can still recall the horrors of Hausdorf spaces, closure... and having absolutely no clue what folks were talking about.
math is taught so poorly. hausdorf spaces are paradise! that is where limits of sequences are unique! compact sets are always closed, and other nice properties. why don't they tell us that?, instead of overwhelming us with abstract definitions.