I'm a Whitney Houston stan so I have to acknowledge her inspiration Aretha as the greatest. I can't rank Whitney number 1 when she wouldn't even put herself before Aretha. Her work on the Sparkle Soundtrack probably influenced Whitney more than her mother Cissy Houston and her cousin Dionne Warwick did.
Mariah has one of the greatest vocal ranges in music ever. She can sing contralto like she did in the beginning of "vision of love" and she can take it up to the soprano stratosphere and play around like she did on "Emotions". The same with Lisa Fischer. When she won her Grammy and tied with Patti labelle that spoke volumes.
I would say
Aretha is number one for being the most versatile. that song I posted with her and Whitney going back and forth vocally, Whitney was hanging with her until Aretha started scat singing Lmao.
Whitney is number two because her voice was elastic, her diction and phrasing always remained clear, her vocal agility and power was unparalleled. Her registers were so connected it's like she stretched her voice like a rubber band that refused to snap. She'd hold a note for 40 days and 40 nights. Had the lungs of a Kryptonian. Her runs were perfectly place fluttered like a butterfly and stung like a bee.
Lisa Fischer is number 3 because she's your favorite singers favorite singer. She was a very sought after background vocalist and her work with Luther Vandross and the Rolling Stones is iconic. Her whistle register was piercing and she could sing like the the other 4 while also dancing.
Mariah is number 4 even though she has the greatest range amongst the people you mentioned sometimes her voice isn't always reliant. Mariah in her prime was unfukkwitable tho. When she is in the zone she is in the zone.
