Clean Vocals or Death Growl? (Modern Prog)

So, regular singing for me. 

It is a very subjective question.   Because the objective answer is that anybody who is not tone deaf can sing.  Carrying a tune is really not a big deal at all, unless the melody is really complicated.   But I have never heard an out and out growler whose melodic singing I could enjoy very much in its own right.   Yeah, not even Akerfeldt.  I honestly find his melodic singing very dull and boring.  Mastodon sort of mix aggressive hard rock/heavy metal singing with occasional harsh vocals and I have maintained that that's a much better approach.  Extreme consonance and dissonance in juxtaposition is usually a very awkward combination (not saying there's no way it can work, never say never).

Leaving Patton out of this, who is a master of many vocal techniques, harsh and otherwise.

Growling and other harsh vocals actually require a great deal of training, that is, if you want to do them without destroying your voice.  You have to go through the entire process of learning singing technique, and then apply that to harsh vocals.  There are professional instructors who specialize in teaching harsh vocals, and there's actually a DVD out called "The Art of Screaming" which goes through all the technique and everything required to do some brutal and varied harsh vocals without blowing your vocal chords out.

Growl, fart and roll - and the whole world's at your feet.