I tend to read multiple books at a time. Personally, I find that I enjoy particular kinds of books more or less depending on the mood I'm in, so it's useful to have a couple kinds going at once. Right now, for example, I'm reading Hafiz's The Gift (a poetry collection), Bertrand Russell's The Problems of Philosophy (an epistemological analysis), Nietzsche's Thus Spake Zarathustra (a moral text), and Alice Goffman's On the Run (a first-person sociological study). Some nights I'm in the mood for Hafiz, but other nights I feel like some moral philosophy. It just depends.