I appreciate fiction, but I almost always read nonfiction. It's probably because I typically choose the books on topics I'm interested in and want to learn about. But I also love the way a great nonfiction writer can weave a narrative so strong that it's just as much literature as it is journalism.
Some of my favorite examples of nonfiction that do this well: Soul Full of Coal Dust, Toms River, Desert Solitaire (Abbey can be problematic, though, so be warned), The Pine Barrens,This Land, and on and on.
I guess I'm kinda stuck in the environment/nature section these days!
Mostly fiction. Studying or working full time means I read to escape, unless it's a textbook. There are many non-fiction books I'd like to try, but I never have the energy.