Bob Stewart may not have brought too much originality to his ideas, but he's had his successes here and there. He brought 4 classic shows to the game show world, one of which is, of course, the longest-running game show on American TV [albeit not in original form].
Merv may not have brought too many games to this world altogether, but he is responsible for the 2 most successful games in syndication. Not to mention, having a 3rd creation on the air at the same time is an achievement not seen since....how long ago???
Tough call, I say, but they're both right behind Goodson.