I far prefer nonfiction. Though not for any smug reasons. People would probably argue that nonfiction doesn’t add anything new to the table and just serves to explain harsh truths. So it’s just a personal preference.
Part of the reason for my preference is that I love history, particularly the history of the 19th and 20th centuries. And I’ve become a bit obsessed about the state of humanity as the decades pass and where the world should be headed, because history has a lot of valuable lessons to teach. I like to use my fictional universe of stories as settings that take place in the real world as it helps me to relate to my characters. Understanding history as its both told and parts that people would never even think to explore help develop a deeper appreciation of class, economy, religion, politics, science, philosophy what have you.