compared to Audible.

Since they added Audiobooks earlier this year, I've listed to 4 books - all by David Baldacci. Looking through their catalog, Spotify has plenty of books that I'll be interested in, so their catalog is plenty for me. I also don't listen enough that the 15 hour monthly limit will come into play very often. So, Spotify is perfect for me.

If you listen to a lot of books, or have specific books you want to listen to that aren't available on Spotify, that would point towards Audible.