I think it depends on how good the singer is, whether or not the song lends itself to being sung unaccompanied, and lots of other factors such as the surroundings, etc. It's only been in the last several years that I started to really enjoy unaccompanied singing but if it's done right it does have the ability to pull your attention in - almost cast a spell over you, as long as you're prepared to put forth the effort to listen. I would tend to agree that, for me, a mix works best. I usually accompany myself on guitar but do sing some songs unaccompanies.