Mine is Strawberry since it has a ton of options and plays a ton of formats. It's also (distant) fork of Amarok 1.4 and integrates well with KDE Plasma. I'm curious what other people are using these days. What's your favorite player?
I used to use Strawberry, but my collection has grown enough that I can't just sync it everywhere, so I use Jellyfin now. I still use Strawberry's library management to move files into album artist/album/00 - track.ext though. Someday I'll dig into id3v2 to just write a script instead.
If you want to continue to use Strawberry, you could stream your music with a subsonic server, Strawberry supports that.
For me it was the other way round: I was using Nextcloud music and searched for a music player on Linux that could stream my .flac-collection via subsonic. That is how I found Strawberry.