Cary Grant - I always thought was underrated as an actor and comedian (see: Notorious; Holiday)
John Garfield - Very compelling (see: anything he did)
James Stewart - Can act sincere like no one else (see: Mr. Smith...; The Shop Around the Corner)
Barbara Stanwyck - The ultimate femme fatale, but equally as good at comedy (see: The Lady Eve or Ball of Fire)
Rosalind Russell - Great comedienne (see: Hig Girl Friday; Auntie Mame)
Katharine Hepburn - Could hold her own with anyone and come out on top (see: Adam's Rib; Alice Adams