Plexamp, my experience + suggestions
I've been using Plexamp for a few months now (iOS, Windows, Linux) and here are my thoughts.
The UI is nice, the configuration options are great, the client runs fast on all my devices, and I really love that it supports the OPUS codec so the downloaded music takes up less space on my phone.
However, regarding the UX, there are a few frustrating things I wish the developers would address.
I primarily use playlists (thats how I used other clients too), so my feedback is mostly related to that, these things might not bother others at all.
The search function needs a rework: currently, it works somewhat like a "first match" mode. If an album name (which is common for singles) matches the track name, it only shows the album in the results. It would be great to have a filter bar at the top of the search (artists, albums, tracks) that remembers user preference. If I'm searching for a track 99% of the time, I shouldn't have to keep switching to it. Plus if theres a match for both an album and a track, this would keep them separated.
Missing playlist search: another search issue is that playlists don't have their own search function. If I’m currently playing a song and want to switch to another one while staying on the playlist, I simply can't search for it. If they added a playlist search, playing a matched track could automatically populate the "up next" queue with the rest of the playlist (following the playlist's set sorting order so it would act exactly as if I had just scrolled down to it and hit play).
iOS left/right swipe: a great UX addition for playlists would be allowing for example a right swipe to queue a track as "play next" (I know you can select "play next" from the context menu, but swiping would be much more convenient).
Quick playlist access from the player: Swiping up during playback gives 3 options: back to, up next, and related. If I'm playing from a playlist, it would be nice to be able to access the playlist itself just as easily as those three options.
Playlist sorting: it would be great to have an option to sort by date added. Since I use smart playlists (so I just have to copy the tracks into the playlist's folder on the media server and they get added automatically), it would be especially useful to be able to sort the list by "recently added" for example.