For me, the armors that Bethesda really nailed it were Orcish and Glass. I can't even count the number of times where I looted those types of armor and I just sold them as fast as I could blink, no matter how good they were in comparison to the armor I was wearing. Orcish armor finally looks brutal and savage, just like the race itself, and Glass looks, well, like actual glass, and has a cool, sleek, design to it.
Now Daedric... On one hand, Oblivion's armor really looked like it was a set of armor that demons would wear, and a person wearing that looked fearsome, to the point where you only needed to turn your head at the general location of the bandit and he would probably just have a massive heart attack out of fear and panic. However, what I didn't like was that it was thick as all hell; I get the impression that they started drawing the concept art and then didn't stop adding details to it, and I'm sorry, but the shield is just laughably stupid. On the other hand, Skyrim's version, again, looks fearsome, damn awesome and I like how it's not symmetric; it gives that impression of something not natural, especially with the spikes protruding out of the shoulders. Still, for me, it looks a bit too... alien, I would say, it doesn't scream "Demon" when looking at it.
I would say that Skyrim, for me, wins in terms of armor design, with the exception of Daedric, where there's a tie.