Just opinion, but: I don't think Davis was that fantastic.
I didn’t find Bette Davis’ performance in this film all that enthralling. Her attempt at a cockney accent was grating and the way she flounced around each scene, trying to steal it with a pose, grew very old, very quickly. I am aware of the fact that Katherine Hepburn turned down the role, but I picture her playing it with a greater depth and truth. I think Hepburn would have been able to balance Mildred’s crudeness with her beauty more comfortably.
Leslie Howard’s performance was beautiful and I believe he was ideally cast. He played the role with an acute intelligence and sensitivity that seems to be present in many of his roles. I’m biased here though; Howard being one of those classic actors I love to pieces.