Having preferred non-fiction to fiction over the years—I change direction—I'm reading one or two fictional works of noted authors of the 19th and early 20th century: Stendhal, Flaubert, Balzac, Proust, Wharton, Woolf, Joyce et al.
Now I'm impressed by Henry James's writing in The Portrait of a Lady. Oftentimes the story or the plot turns on what his characters say to one another; he writes an easy-flowing, but revealing, dialogue. It's so modern in tone it surprises one that it was written in the late 1870's.
James made it easy for the screenwriters who followed him to adapt the conversational portions of his work.