Robert Mitchum is up there, but no one can touch Cary Grant for me. I may not care for all of his films, but he's great in every one of 'em! That said, Robert Mitchum is incredibly underrated. And I have a magic 3 from the Pre-code era: Ricardo Cortez, Lyle Talbot & David Manners. I watch anything they're in!
And for the ladies, I'm pretty cliched...Joan, Bette & Stanwyck, from Pre-code all the way to the end! But there can be a big difference between actresses & performers. My all-time favorite female movie star is Rita Hayworth. In fact, I have a signed, numbered George Hurrell portrait of her. She's luminous, probably the most beautiful woman I've ever seen. And when she dances, she is either joy or sensuality personified...sometimes BOTH lol!