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 don't really love any that I've tried so far, but I dislike Audacious the least. FLAC, Musepack, and ReplayGain support are requirements for my library.
The last one I loved was foobar2000 on Windows, which supplanted Winamp. Linux UIs mostly feel a bit clunky by comparison. When the window has focus I like to have spacebar for pause/play, arrows up/down for primary gain, and arrows left/right for seek.