I dunno about all the nuances and functions, but I've been using WinAmp for years, and find it the most uncomplicated for just simple playing of mp3's, of which I have ....er.... lots.

Just load up a folder, and it will play the folder. Toggle shuffling, and it shuffles. I used to use it for saving mp3's to .wav format to burn to CD's, but now that DVD players can read mp3's, I don't bother anymore.
I've tried QDC and WMP and iTunes. Never really gave them a total workout, because I am so comfortable with WA, I always just go back that. I've never tried Sonique.
I do have a question though. Which player do you think uses the most computer resources? I think that usability comes down to that when I've got my sorry old puter loaded up with Photoshop, Irfanview, and a media player. I do find, however, that once I load up some music into WA, then minimize it, my computer runs better. Then, I just operate it via Sysmetrix until I need to load up some more tunes.