Good question, although I don't really know the heroes of the smaller lines.
DC: Batman and the JSA tie for #1. Also Moldoff's Hawkman, Meskin's Vigilante, Scribbly/Red Tornado, Simon & Kirby's Sandman, Boy Commandos and Newsboy Legion. Timely: S&K's Captain America, Everett's Sub-Mariner, not much else really Fawcett: The Marvel Family!!! Quality: Plastic Man, Uncle Sam, Crandall's Blackhawk Dell: Tarzan, Lone Ranger, Popeye
Having read the first Golden Age archive, I found the original Sandman to be one of the Golden Age's most interesting, and creepy, superheroes. I love Kirby, but turning him into a generic tights wearing superhero set the character back decades.
Grand Dictator for Life of the Classic Comics Christmas
Simon and Kirby did not change Sandman. They came onto the strip several issues after the change. And while from our vantage point here in the 2010s, it looks like a huge mistake, the change made the character more popular in the '40s by several orders of magnitude.