Hmmm.... from the list, I guess I'd go with "A Whole New World". But to me, a pretty smooooooooth cut, you have to put in Luther Vandross. And of his duets (and he has some real powerful ones), I'd go with "I (who have nothing)" taken from his "Power of Love" CD back from I think 1990 or so. Now that's a soul ballad.
Ironically, this song has been cut up and remixed on a cd titled 'Brazilectro vol. 4'. I even reviewed that CD about this time last year both on this site + on Amazon.com. It was the strangest cut on the CD... borderline creepy to me. Now I know why. Speaking of Brazilectro vol. 4, there's a nice duet on there by Justin & Janice Andrade titled "Running To You". It's sung in English and Portuguese.