One can transport you to other worlds, while the other can tell you more about the one we inhabit. What’s your preference?
It’s hard to choose, of course, as picking one over the other excludes a vast swath of some of our best writers — imagine having to give up “The Great Gatsby” on one side or “A Brief History of Time” on the other. Fiction can comment on the real world, but can nonfiction be as imaginative as a novel? Depending on the writer, maybe: Truman Capote envisioned “In Cold Blood” as the first “nonfiction novel,” a title it lives up to by being as extensively researched as it is elegantly written. Maybe there’s more of a middle ground than you’d think.