As far as unique weapons (named ones) I have no clue. All weapons are tiered based on the material used in them.
So the best warhammer in the game would be a Daedric warhammer but those aren't dropped by enemies, just found in chests. Daedric weapons though are extremely rare. You can smith one with the proper perks and a smithing skill of 90 or higher. Otherwise go with an Ebony warhammer