Most pie recipes I've seen call for multiple varieties, especially from different categories http://frugalliving.about.com/od/foodsavings/qt/Best-Apples-... My grandmother used mostly Braeburn and Northern Spies, my mother uses Crispin and Granny Smith. I think a crumble might break down the apples more than a pie with its protective crust, so harder varieties might work better there.