I will say Beyonce as my opinion. Mariah has only the whistle note over Beyonce. Beyonce runs and riffs are better than Mariah's. They both are great though

Beyonce

Mariah by a country mile.

Mariah By far
When will Bey give vocals like Mariah did in You Don't Know What To Do ending?
Never!

Mariah by FAR.

beyonce's inspiration a.k.a mariah

Not again

To answer to the OP: the better voice is the one of the best vocalist of all-time aka Mariah Carey

*I love Bey too, don't get me wrong

Bey is the best female vocalist of all time, Mariah is the one of the worst female vocalists of all time.

Says her 5 octave range and vocal agility and duets with Whitney Houston, R Kelly, and Luther Vandross

Beyoncé, in my opinion.

This is tough though. I wouldn't disagree with anyone saying Mariah.

Bey.

Lol
Girl It's 2014
You can't use that anymore

Beyoncé.

Mariah would win if this was like 9 years ago tho

"Beyonce runs and riffs are better than Mariah's" - I'm going to disagree with this. There are some vocal feats that Mariah sung in "Heavenly, "The Art of Letting Go", and "Cry." in her last album (May 2014) that Beyonce hasn't even dreamed of replicating. Beyonce STILL doesn't have Mariah's agility or fluidity throughout her range. Not only is Mariah's melisma much more complex/difficult, incorporating the craziest fiortura phrasing in the simplest of songs.. This is simply the truth..Listen for yourself

https://www.youtube.com/watch?v=i-a2JwEkviU

and

https://www.youtube.com/watch?v=Wfv5E6b6ZUM

Beyonce just doesn't have that level of coloratura skill..Not to that extent. Mariah's melisma is on another level.

The best vocalist of all time is the better vocalist.

And Beyonce admittedly stated that Mariah influenced her especially in terms of riffs and runs.

Mariah still hit notes in 5 octaves on her last album so clearly she's still got it.

Mariah by far