Musicbee is the only player that has all the features I need to sync a random selection of tracks to an android phone. A couple things that I'd like to see however:
A progress bar while syncing. Not anything detailed, just something to give me an estimate of how much is left.
Resume/Retry Syncing: the ability to pause syncing e.g. a certain playlist, and then resume later, instead of syncing everything, and to retry syncing songs that failed for one reason or another last time. I'm not sure if it does something similar when simply copying, but it doesn't seem to when the songs have been converted. It just asks me if I want to delete what's on the device.
As far as I can tell, Musicbee recognizes when the same device is connected, so it would probably be pretty simple to create a local database of what songs successfully synced, and cross-reference with what is on the list to be synced. The only thing with that would be a simple "reset database before sync" checkbox in case we do want to resync everything at any point, or completely change our playlists.
It'd also be a nice bonus if it could intelligently delete songs from the device based on playlist changes, but that's honestly a non-issue with me if the resume is added.
Musicbee is by far the best music player I've tried, so keep up the good work!