Don‘t know about the US market but in Germany there were many audio books available in Spotify already that you could access via the normal premium subscription. Few days after I read about the launch of purchasable audio books in the US all of those vanished so I canceled my subscription and got Apple Music via Apple one which was a little cheaper for the whole family when adding the extra iCloud storage I needed anyway. Happy with the decision so far. I just had to move all my playlists to Apple Music which was easy due to a random online tool I found