I voted for Maggin, I think when you look at his comics and novels, he set the path writers like Moore and Morrison would explore. I think Cary Bates deserves a mention for the Immortal Superman and Who Took the Super out of Superman.
With Alan Moore, I think you have to include Miracle Man and Supreme as well.
In addition to Mary Pasko, I would add Gerry Conway and Len Wein. Conway for Superman 301 which is the greatest Superman Vs. Grundy match up ever, and the best Hulk vs. Superman comic out there. Len Wein for his Mongul stories and the Man Who Murdered the Earth. The last comic was the earliest mention of string theory that I had ever heard of, and it places Superman as an extra-dimensional being that rivals Dr. Manhattan.
I think fans of All Star Superman should read the original Superman Red Superman Blue and the Last Days of Superman by Leo Dorfman and Edmond Hamilton. They really take Superman to the extreme as to how he could change the world.
Speaking of which, Jerry Siegel kind of explores those themes with his Mxyzptlk stories and How Superman would end the War.