Simply the best.....(again)

The other day, a friend and I were having a discussion (more of an argument, really), about who we considered had the finest voices of all time. So - how do you rate my choices?
First and easiest - contralto. No contest, has to be Kathleen Ferrier. No one else comes close.
Next - bass. Bearing in mind that we are just considering the voice, not the technique, again for me pretty easy - Paul Robeson. I had an uncle who was into voice training, and he always maintained that the two most perfect voices in the world were Robeson and Bing Crosby, both of whose singing voices were, as he saw it, just extensions of their speaking voices, and they could slip from one into the other without any apparent conscious effort.
Tenor, and now it becomes more difficult, not least because there are two distinct sorts of tenor voice. You have the full-blooded powerful "Italian" type tenor voice which is always forced, even when singing pianissimo (think Harry Secombe - of beloved memory) and the purer "head" type tenor voice epitomised by such as Heddle Nash, Peter Piers etc.. I go for the one man who seemed capable of producing both to the highest quality - Bejamino Gigli.
Most difficult - soprano. There are so many top class sopranos to choose from, and I had big problems in defending my choice to my friend, because she was a performer who was eminently capable of producing a BAD performance, and did so on many occasions. But, when everything was right with her (which wasn't all that often) she had a voice which was in a different street from all the rest. If you can accept the blemishes, then my choice is Maria Callas.
So that's my opinion - what do you think?