Quality is always my first choice, with Fawcett running a distant second place, however, most any publisher represented here published something worth reading with very few exceptions.
Quality not only had same great characters (Plastic Man, Blackhawk, Doll Man, Kid Eternity, Captain Triumph, Black Condor, etc.) it also had some wonderful obscure characters (the Whistler, Scarlet Seal, Dragon, the Voice, Ace of Space, Blimpy, etc.) who were highly original and entertaining. Basically, Quality produced very little work that wasn't among the first rank, and they had writers who could tell complex, intriguing stories in the space of five pages without making them seem contrived or curtailed. I doubt we'll ever see the likes of a single publisher who had so much to offer again.