Disney characters via Dell (Mickey, Donald, etc...)
Captain Marvel & Captain Marvel Jr.
Superman
Batman
Sheena
The "All Star" characters (Wonder Woman, Green Lantern, Flash, etc...)
Timely-Marvel characters (Captain America, Submariner, etc...)
The Spirit
That's more then ten, but it leaves out a huge number of very popular lesser characters (from today's perspective... back then they were huge) like Plastic Man, Blue Beetle, Hangman/Black Hood, Doll Man and The Blackhawks just to mention a few. And then there's various newspaper comic strip characters via Eastern and Dell, and the pulp crossovers like The Shadow and Doc Savage.
The GA was such a time of great creativity in the medium that it's hard to narrow it down further than that IMO.