[size=small]The question seems very unfair since virtually the whole industry (recording, mastering, etc.) is slanted towards speaker usage. With all the industry bias towards speakers, most are going to select them as the favorite. Most of the folks who choose headphones, select them for the same reason I do - because you want to avoid disturbing others.
If there was a competing headphone-based industry (recording, mastering, etc.), the results here may be much different. Compare the best of the speakers in a conventional system to that of headphones in say a binaural-based system and then you have the basis for a healthy discussion.[/size]