First, there's Curt Swan, who drew Superman during 1960s, 1970s, and 1980s. I don't think he'll ever be topped. His art was especially good when inked by Murphy Anderson.
Next, there's John Byrne, as a close second. He didn't have anywhere near Swan's track record on the character, but his breif tenure during the mid-1980s was very impactful and carried the character through the 1990s.
Gil Kane didn't do a lot of work on Superman, but the stories he did draw (in Action Comics and a couple Specials in the 1980s) were spectacular!
Finally, there's Jose Luis Garcia Lopez who, sadly, spent most of his career in DC Comics' licensing arm drawing style sheets and merchandising artwork, but he drew some spectacular Superman team-up stories in early issues of DC Comics Presents. I'm ending this survey of the Man of Tomorrow's yesterdays with a drawing from his that shows Superman's changing looks from his debut in 1938 through to the 1990s.