As long as it's deep, it doesn't really matter:
These don't really match your criteria but anyways, my favorite runs in Engelberg are the Laub, Steinberg and Galtiberg. None of these are groomed but they are sure fun when the snow is good.
Steinberg
Galtiberg
As far as groomed runs and fantastic scenery, you can't really go wrong with the Gornergrat area in Zermatt: