...as far as I'm concerned....
Concerning actresses: Female
There is no actress today that could even come close to the acting skills of Bette Davis. A singer she was not. However, for the Baby Jane picture her singing was perfect. (could this have been acting too?????) Jessica Lange, Glenn Close, and Meryl Streep come close, but no cigar. When Bette acted, you completely forgot who she really was. THAT'S ACTING.
Concerning Opera Singers:
What can I say, since Maria Callas died, there just hasn't been one. Period.
Other opinions later.........