If you mean "now," I'd say Headley, Errico, Krakowski and Chenoweth are all beauties.
But if you mean "of all time"... I'd go way back. WAY back.
Heck, at the turn of the (last) century, it was Lillian Russell and Billie Burke.
Moving up half a century, in the 1950s it was Audrey Hepburn... and other amazing creatures like Julie Newmar or Jayne Mansfield.
In the '80s, Bernadette reigned supreme. No one held a candle to her.
So... there's a few random answers throughout history!
"Jaws is the Citizen Kane of movies."
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