I *swear* I can hear a noticeable upgrade in quality when using Foobar as opposed to iTunes....but its possibly just a placebo effect.
I used to hop between players and spent countless hours testing configurations, etc.
I just went back to iTunes.
Cause for me, I just want a library that holds my music, and syncs with my iPod/iPhone. All my real listening I do on my iPod Classic or through a system, so my library is optimized to deliver that experience.
I guess it just depends on what you want to use it for, or how how much time you are willing to spend tweaking settings and discovering new features. Or where you spend most of your time listening to music.
I stopped worrying about my library, and instead started focusing on the actual files(quality, metadata) and the playback equipment used.
Granted though, I painstakingly enjoy organizing my music library.
Some people have rock gardens. My zen garden is my iTunes library, or my off-and-on relationship with Foobar.