This is impossible. I'd fill up a top 10 before I passed the Golden Age authors and there are all kinds of superb writers of short fiction for short periods, such as Zelazny in the 60s, Tiptree and Varley in the 70s, Cadigan in the 80s and Chiang in the 90s and on who, while they may have written a great novel or more and may have published a thing here and there outside the peak period, can't really make a list like this but really deserve some kind of mention. So I tried to pick favorite authors yet also be at least somewhat temporally fair. Even aside from all that, there are still a dozen or two authors I could put on the list as easy as some that did make it. And I did cheat anyway and come up with 11 - I couldn't leave van Vogt or Sturgeon off even though they imbalance the list to the Golden Age but I didn't want to bump a later author for them either. And, as always, this list can change unpredictably at short intervals.
*deep breath* So...
In order of first professional SF publication:
Isaac Asimov
A.E. van Vogt
Robert A. Heinlein
Theodore Sturgeon
Arthur C. Clarke
Algis Budrys
Norman Spinrad
Vernor Vinge
John Shirley
Bruce Sterling
Greg Egan
The
SFE has articles on them all, too, of course but, oddly, the wikipedia articles are usually (though not always) better in a lot of ways.
But what is this list? How do you pick it? The authors I have the most books of? (So where is Cherryh who is in the top 10 of "most numerous books"?) The authors who've written some one or two examples of overwhelming brilliance? (Where is everyone from Daniel Keys to Robert L. Forward?) The authors who've written the most consistently for the longest time? (Some of the authors I listed didn't last a whole career so why are they here, then?) And so on. I just picked people who I have a lot of books of, or at least a lot relative to their total, over a significant span of time, that I liked most of a great deal, who have at one time or another really lit me up with something or affected me in a personal way, who didn't have much bad to significantly counteract the positives. Is that more or less how you folks picked yours? Or other criteria? Or'd you just wing it and I'm taking this way too seriously?