I don't if this site is any good at all but it has a chart about the apple varieties. According to it, the best ones to use for Apple sauce are the Galas but I think it would be fun to experiment with different types of apples and compare the flavors.
Granny Smith is always what I use, because it's nice and tart and really stands up well to the heat from cooking. It makes the absolute best apple pies and tarts too. But, if you don't like a tart sauce, you can use Red Delicious, it makes really good sauce that is nice and sweet. I don't always mash it all up either, I leave a few chunks, makes it a little tastier.