@Omni
Droning sounds singular sustained notes do have a discernible melody: the single note that they are sustaining. That's why I usually prefer vocals which are not just sung at a single pitch but which alter in pitch to create a variety of diverse melodies.
Again, I'm not saying that harsh vocals are literally percussion in a technical sense, I'm saying that they often serve a percussive role in the band and therefore are related to the sound of percussion. Most, if not all, non-melodic instruments are considered within the percussion family.
@CASSETTEISGOD
Again, the reason I feel that clean vocals are more diverse than harsh vocals, is because harsh vocals are very limited to the degree of how much melody they can deliver. While it is true that they can alter in pitch from lows to highs, their overly distorted nature drowns out the melodic pitch of the note they're delivering, making each lyric sound essentially the same.
It is of course, a subjective opinion whether someone prefers harsh or clean vocals in metal. What I'm doing is trying to explain rationally and reasonably why I feel clean vocals sound better than harsh vocals, not to objectively prove that they do, since that would be undoable.