Here is another option to consider: audiobooks take up a lot of space and even with the larger storage on our current phones, you might not want to fill them up with audiobooks. If you are going to go the route of downloading books in MP3 format from any source to your computer, consider Audiogalaxy to stream the books straight to your phone (not a cloud service like Amazon Cloud Player or Google Music, although those are alternatives as well). With Audiogalaxy, you just install the app on both your computer and phone, select the folders you would like to link between the two and you are good to go. It buffers pretty well, and you can even "pin" as many tracks as you like if you think you are going to be away from a good signal. This temporarily downloads tracks to your phone for offline listening, so you get the best of both worlds. One catch: your computer has to be on if you want to stream, but you can "pin" tracks if you need to turn your computer off.
I have listened to audiobooks for decades (literally) starting with actual tapes in a Walkman, and I have tried everything. Audiogalaxy is my current "go to".