I’m using the IOS Libby app from OverDrive.
It’s similar to the old IOS Overdrive app, but is somewhat newer. Perhaps better.
And it works well. Overdrive was horrible, terrible, hilariously bad for many years … but they finally figured out a good interface.
The selection of Audio books available is in 2018 quite good. Better than in the past. I have no problem finding things I want to read.
I wait anywhere from 2 – 12 weeks for a book to arrive. The library sends email notification when it’s available.