It's tough to determine what the best sci-fi book is, as there are so many great ones out there. However, some standouts include 1984 by George Orwell, Brave New World by Aldous Huxley, Dune by Frank Herbert, Ender's Game by Orson Scott Card, and The Hitchhiker's Guide to the Galaxy by Douglas Adams. All of these novels are considered classics in the genre, and offer readers fascinating looks at different aspects of society, technology, and the future.