I hate her as a person but Maria Carey has a beautiful voice with a HUGE vocal range. Her mother was an opera singer and made sure she had the best classical voice training available starting very young in life, and it shows. Very few women can match her vocal abilities.

For pure energy I don't think anyone has worked harder with Madonna, who I also dislike, who has done as much as she can with as little as she has. She is an example of what pure determination can accomplish.

For pure beauty of a voice though I have to go with Whitney Houston, who also had a huge vocal range. For some reason her vocal cords resonate in a way that just reaches into my soul. A very troubled person with a life that was cut short ... but still had a beautiful voice.