Given a 5 minute song, if I have the choice to download a 11MB file (320kpbs MP3) or a 330MB file (24/192) I would of course choose the 11MB file. The sound quality is perfectly acceptable and the file size much more convenient to manage (storage, backups, etc.).
In terms of the convenience of managing the file size and sound quality I think 320kbps MP3 is the best compromise.
Here's a file size comparision of a 5 minute stereo song:
MP3 128kbps > 5 MB
MP3 320kbps > 11 MB
Uncompressed 16/44 > 50 MB
Uncompressed 24/192 > 330 MB
When talking about sound quality there is a much more relevant issue: the amplitude compression (distortion) abuse used by mastering engineers and producers that totally destroys the dynamic and life of the sound. That is a real issue. When buying a song there should be two versions to choose from:
A) "Loud", dynamically destroyed / distorted version.
B) Normal, dynamic, non-distorted version.
Today only version A is available to buy.