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?
+1 for Cantata! Although it's not maintained, there's really nothing missing from it. It's complete as it is! Plays anything and you can also have your podcasts and web radio stations in it.