I've used both Foobar and MusicBee (on Windows) and personally I prefer MusicBee's interface. It works well with my library of 21k files - not sure how it performs with libraries much larger.
The beauty of foobar2000 is that you can lay out the user interface however you want. The built-in layout editor is very intuitive, and the UI can be extended or even replaced with numerous third party components.
I'm a huge MusicBee fan. For my money, nothing touches it. It's running on all my Linux boxes (via wine 7.x) with playlists and music kept in sync using Syncthing. I would love to be able to use a native Linux app, but they all suck in comparison.
The website talks a lot, but where are the screenshot? Are they afraid to show what it looks like?