Depends on the artist. I don't think this has to do with negative or positive feelings, but rather the intensity of feeling invested in the work that makes the difference. "Clarity is not one of the properties of emotion" Titcherner.
The Aesthetic effect moves in two directions at the same time:

I would say it comes from stronger emotions. Mainstream art (especially music) frequently commercializes positive emotions, making for weak art, but negative emotions aren't immune from it. See Five Finger Death Punch.

I think a good proportion of them do too. Also on shows like The Voice and American Idol talent comes from performers from the toughest backgrounds, those who have experience pain and loss and struggled to reach existence. Songwriters as well.

This would depend upon which emotions stimulate creativity in an individual, as well as which appeal to the one appreciating the art. For me, it just depends upon the mood I'm in at the time I'm viewing or creating.