Right now I am in the mood to say Vision Of Love is Mariah's best song. But if you ask me next week, you'll probably get a different response.
I love, love this song.
And I do believe she's a superb vocalist. This video alone shows you her full vocal arsenal.
If you listen really carefully, you would think Mariah is four different persons doing the harmonies. She shifts from chest to whisper to head register in just a snap. Amazing.