Personally, I prefer to have absolute peace and quiet while I'm reading, mainly because I feel that it distracts me and takes me out of the moment of whatever part I'm in. I can still understand and read through the book, but depending on what's going on around me, it can end up spoiling the type of emotion the author is trying to get across to me at that moment. It's one of the things I completely hate to have to lose.
However, saying that, I don't completely mind music when I read. It just has to be something low-key, preferably with no vocals, and in the background where it can simply just melt away if I want to completely focus on what I'm reading.