Malog Bal's Dreaded Mace
I love the power, you can temper it to become even stronger, the effect is nice and the guards and townsfolk freak out when you carry it.
Usually I like to use whatever I'm in the mood for during that playthrough, such as if I want Imperial, I'll settle on the Imperial stuff, boost my Smithing and Enchanting enough to make some damage. I love the Stalhrim set from the Dragonborn DLC and the Crossbow from the Dawnguard. I especially love combining Stalhrim and a Frost focused spell sword. Just screams Ice damnation.