The 90s version of Marmite, Brandy possesses a divisive voice - one either loves it or hates it. For those that love it, Brandy's oft-noted for her deep, rich alto, surprising range and terrific studio harmonies. One of the most influential singers of her time.
Seal isn't brought up much in discussions like this, and that's a shame. He does what great vocalists are supposed to do - use dynamics. He keeps things close to the chest, then explodes.
Although not thought of as a vocalist, in the traditional sense, Kylie is one of pop music's greatest interpreters of lyric - no one vocal sounds like the next. This speaks to Husky's praising of her "versatility." Some examples:
Like a fine wine, her voice gets more textured - and better - with age.
I don't think her voice is like... one of the BEST of all time, but it does have this angelic quality to it that sets her apart. and in that sense she's underrated as a vocalist.