My favorite Music app version is 8.4.1. I think it's the best blend of iOS 6 we're going to get in a post-iOS 7 world. 6 was of course the cleanest, most intuitive, and least "bloated" Music app in iOS 6 history. But I enjoyed the UI upgrade in 8.4.1 and found Apple Music pretty easy to ignore once I turned it off.
iOS 7's Music App was garbage. I understand they wanted a complete UI overhaul, which is to be expected over time, but they literally broke some of the most basic and intuitive functions of the Music app in the process. I won't rehash it here, we all lived through it.
8.4.1 more or less fixed what 7.0 broke, in my opinion. Simple things like a return of nested albums for any artist with 2 or more in your library; shrinking the Artist images to allow more on screen, etc. For me, it felt like MY music app was back. I was never going to get iOS 6 back, so this for me was pretty solid.
9.2.1 began to break the app again. Simple things like nested albums got expanded if the Artist has less than 4 albums to their name in your library, returning to the endless scrolling between albums to find a single song like we had on 7. The UI is getting crowded, too many little icons like that phone with a check mark, hearts if you "love" something or not, and the lockscreen touch controls too close together, making a simple volume adjustment a real chore sometimes.
I don't know why this app is so difficult for Apple to keep stable and consistent in a post-Jobs world. I hope iOS 10 returns to the clean experience and functionality we had in 8.4.1 or 6.0. But I'm not hopeful.