Above: This pretty graph shows how each publisher weighs up against its rivals, based on the success of its in-house studios
Nintendo! By a not inconsequential amount, given the method we used. Of course, there could be some anomalies, given we're working with averages of averages here.
For instance, EA has lots of fair-to-average studios that pull its score down. While the actually brilliant Rockstar gets a bum deal because of Table Tennis' limp performance on Wii, people not reacting well to Manhunt 2 and having problems with Vice City Stories. Add the less recent Bully or the (quite different) Xbox 360 Table Tennis, and it would be a different story.
But, crucially, any developer is only as good as its last game. Or, in this case, its last three. Nintendo's remarkable consistency puts it right ahead of the pack, with the sublime Mario Galaxy just another example of the Big N's reliable quality. Looks like the others need to pull their socks up...