WMP, RealPlayer, VLC and WinAMP - each seems equally fine for playing media. I doubt there's much difference between them. They're all free and play the same files.
There was this time when my old XP desktop stopped playing sound under one of its three accounts - VLC was the only program that could play any sound.
I almost never use QT - it comes w/iTunes, and I think is only needed for playing Apple video formats.