It's a tie between steel and Dwemer(Dwarven) for me.
I made my own Uber mod and stuck a barrel filled with the stuff next to Foryn Gilnith, but I keep seeing barrels filled with that stuff popping up all over the place. And a shopkeeper was trying to sell me a one-handed ultralight Dwemer Claymore to me the other day. (Go ahead, make a one-handed Claymore. It looks so cool with a shield.

) So be careful with your mod.
Now for the armour, steel cause it has this knightly look. And Dwemer cause it makes you look like some kind of robot or Centurion.

Too bad its protection is a bit outdated. Actually, both of them aren't great protectionwise.