It depends upon the circumstances. I also use Umbra quite a lot, but the Sigil stones are also levelled and can be used to create some pretty powerful items - +50 magicka, +10 Strength or +25 shock damage and so on. Shock weapons are very useful again Daedra and Dremora. I've just completed a quest and found that the guy I killed in combat dropped 573 Daedric arrows and hundreds of Glass, Elven and Silver ones! I'm not sure what I'd get at lower levels!
Other useful stuff at higher levels are the Amulet of Swords (+25 Blade and 33% Reflect damage), Amulet of Axes (+25 Blunt and 33% Reflect damage) and the Mundane Ring (50% Magic resistance and 35% Reflect Spell). It's great watching an opponent hit you and then fall over
Daedric Armour is about 25% better than the Ebony equivalent - eg. Ebony Cuirass gives base armor of 15, Daedric is 18.75