The most beautiful actress of all time is hand down Vivien Leigh:
I like Vivien Leigh so much, even more than Heidy Lamarr. Vivien Leigh wins because of her mannerisms too, she is already incredibly beautiful, and with the mannerisms she goes to the next level.
Ava Gardner is probably the most beautiful, and Marilyn Monroe the most sexy, but they are not my type, for me it is Vivien Leigh. She was Cleopatra, and she was Scarlett in Gone with the Wind.
A runner up will definitely be Olivia Bussey who played in Romeo & Juliet:
From today my favorite is probably Alexis Bledel, the girl from Gilmore Girls:
But I also like Julia Goldani Telles:
Emily Blunt has been beautiful in many occasions too:
Honorable mentions would be young Natalie Portman, young Jennifer Love Hewitt, young Sarah Michelle Gellar, Keira Knightley, Mila Kunis, Demi Moore, Jennifer Connelly, Olivia Wilde, and Winona Ryder.
In terms of blondes definitely Bo Derek, Sharon Stone, young Alicia Silverstone, young Cameron Diaz, Kristen Bell, Charlize Theron, and Elisha Cuthbert.