Adele - Has great control over her voice. In the days of 19 that would be a different story though.
Beyonce - Also has great control over voice and knows her own range. She seems a bit showoffy sometimes, but she has reasons to be.
Celine Dion - Has control, but lacks some striking conviction and emotion that the others have.
Christina A - Has little to no control over her voice and does not know her own range.
Kelly Clarkson - Isn't a very strong vocalist.
Mariah Carey - Voice has gotten weaker with age. It's something she needs to work on. She needs to learn how to control her voice with a more limited range.
Jennifer Hudson - Has a strong, convicting voice. Doesn't necessarily have the best control, but it's better than some others on the list.
Whitney Houston - Has utterly destroyed her voice after drug addiction. A true shame since she could have still had the voice she once had.