I think if Bertolt Brecht were alive today, his answer to the question would be, "Ethel Merman."
Apparently...when Brecht and his wife Helene Weigel were in New York in 1948, they attended several Broadway shows, including the original production of Annie Get Your Gun. Merman had a famous running gag every time she saw Frank Butler: She dropped her jaw and stared, as if she had never seen anything so beautiful.
If legends can be believed...Helene Weigel was so taken by Merman's long, slow, slack-jawed take that it became the basis for Mother Courage's famous "silent scream."
Weigel told producer Cheryl Crawford that Ethel Merman was the only "indestructible woman" she had ever met, and thus, the basis for Weigel's characterization.
By way of confirmation, Glenda Jackson also said that Lotte Lenya once told her that Weigel's nickname for Merman was "Mother Courage." According to Jackson, Weigel saw Mother Courage as having Merman's "big, blousy" quality.
In 1961, Cheryl Crawford and Jerome Robbins were (inexplicably) contemplating a Broadway production of Mother Courage, and they asked Weigel who should play the title role. Weigel's response: Merman.
Weigel as Mother Courage:
Merman as Annie Oakley: