Originally Posted by Legion Argentina
Maria Callas is the best female opera singer
Well, she's the most famous and probably the most influential and single most important singer in opera, female or male, of the 20th century. To say that she's "the best" is to some degree a matter of taste. It depends a lot on whether one prefers a singer who sings with lots of drama and passion or someone who sings as beautifully as possible. If one prefers the first option, Callas is your gal. If you prefer beauty of tone she isn't. In that case you're better of with Callas' main rival of the day, Renata Tebaldi. Callas' voice had a metallic quality about it, and later on she sang her high notes with uncontrolable exaggerated vibrato (a wobble in fact).
Another thing that makes a comparison between different singers difficult is that they have different types of voices, and thus tend to sing different works. Callas for example is pure genius in belcanto stuff from Bellini, Donizetti and Rossini and a brilliant Verdi interpreter, but she would be far less effective in, say Mozart or Richard Strauss. That's Schwarzkopf's territory (along with art songs).
Maria Callas, Elisabeth Schwarzkopf, Rosa Ponselle, Kiri Te Kanawa, Mirella Freni, Renata Tebaldi, Kirsten Flagstad, Leontyne Price, Montserrat Caballé, Joan Sutherland, Lisa Della Casa, etc...They are all fab in their own way.
One very important currently active soprano that's not listed here is the great Renée Fleming. She's in her prime now, only has to open her mouth and a beautiful sound comes out of it. She already ranks with the all time greats IMO.