"Al dolce guidami" from Anna Bolena

Maria Callas.  

Modern bel canto singing starts with Callas.  This role was written for Giuditta Pasta, a singer who is now considered a mezzo.  Perhaps it validates my opinion that Callas was also a mezzo.  The aria only goes up to an A, and already she shows a wobble.  Overall this is an outstanding performance with great simplicity.

Edita Gruberova. 

Gruberova does more with the rhythm than anyone of this group. The army of commenters all seem to want to critique the sound of the singers' voices. They never say what they like. They just trash the one you're hearing. I'm far more interested in the style and like Gruberova more here than some other places. She is a very creative artist. She has announced her departure from the Bavarian State Opera because they don't use her much now. She would like to continue singing.

Montserrat Caballe.  

Begin 4:20.  From the comments I begin to believe that those who make nasty cracks like voices no heavier than Caballe.  This is elegant and sweet.  No one would mistake her for a mezzo.  Of course, if you sit around reading YouTube comments, you know that someone will mistake anything.

Anna Netrebko. 

If Pasta was a mezzo, she might have sounded more like Trebs than most of the other ladies. This is Netrebko after the baby, and my sense of this is that she is struggling with her new voice.

Angela Gheorghiu.  

Begin 4:08.  For my ears Angela is one of the most stylish singers that ever existed.  No one slides better.  She draws me, but also has quite a light voice. 

Joan Sutherland 

This is just for fun.  Everyone has their opinions.  After reading the latest study, perhaps the supercritics all live in Louisiana and Texas.  The most favorable ratings seem always to go to the most boring performances.  What fun is that?