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?
Rhythmbox is great and works well for editing tags for my 15,000 track library. I went to Lollypop for a while trying to get some more features but I ended up back at Rhythmbox.