I often read several books at once. Sometimes, when I'm not very engrossed in a book, I'll quit and start another. I might return to the book later, or not.
Mostly I read genre fiction, fantasy, science fiction, mystery, historical mystery. Within those limits, genre doesn't matter much. I might read several fantasy books successively, or switch between genres... it's not very important for me.
Sometimes I may even read a historical romance or two, although I'm not really a romance reader. What I almost never read is literary and contemporary fiction (contemporary mysteries I do read sometimes). I'm just not interested in those.
I don't read short stories or anthologies either. It must be a novel, or nothing.
But occasionally I do read nonfiction.