If you are wanting to improve your actual reading ability then you should be reading physical books. However, if you are desiring to increase your time spent consuming the written word, audio books work fine for this purpose. I enjoy sitting down with a physical book when I can but this isn't always possible. The portability of an audio book is beneficial for people who can't sit and read a book all day.

I agree with the previous comment. Start with books that grab your attention and that you enjoy reading. I find that some of the material that if consumed would make you "well read" dreadfully boring and hard to get through. Unless it interests you it will not help build your love for reading.