I mostly read one fiction book at a time. I read lots of other stuff while I have a fiction book going even though I read as much as a book every 2-3 days. Occasionally I'll pick something else up while I'm in the middle of something but it's more likely I'll drop the other book for a while. I just like being immersed in one story at a time. My one exception to this is for years I used to have a book I was reading along with the kids.