What a loaded question!
However, I'd say my favorite book, in terms of just one I could read over and over again, would be a 4-way tie between:
1. an anthology of Icelandic Sagas (Egil's and Njal's especially)
2. The Tale of the Children of Hurin, Tolkien
3. The Napoleon of Notting Hill, Chesterton
4. Cyrano de Bergerac, Rostand (technically a play; whatever)
