Just my two kilobits: I also prefer FLAC and Ogg and Opus, and after some testing I settled on 24kbps mono Opus for audiobooks and 96kbps stereo Opus for anything more than spoken. I was limited by storage on my old Android device, and my earbuds were whatever. I now have better headphones (~$60?) and speakers (~$130?) and am sometimes transported back to my teens and the wonder of listening to music in all its breadth and depth.