Daedric Sword, my 1h is only like 55, and my daedric sword does 350+dmg, no joke.
Heres how you do it.
Get enchanting, smithing, and alchemy all to 100, and take the 20,40,60,80,100% perks in all three skills. Get to daedric weps in smithing, then go all the way up the middle to the 2 enchants/per item perk in enchanting, and up to the 25% bonus for all beneficial potions in alchemy.
Now, use enchanting to make yourself a set of clothes/neck/ring/head/gloves that gives you +100% alchemy and smithing(obviously be sure to use grand soul gems). While wearing your clothes, make a potion that increases smithing. With clothes and alchemy perks, the potion should make your smithing 100% better.
Now, since your daedric weps perk in smithing lets you improve daedric stuff 100% more than normal, and since your clothes increase smithing by another 100%, and the potion yet another 100%, you can now improve daedric weapons to be at least 350% better (if not more) than they would ordinarily.
Having done all this, depending on your weapon skill, youll have a sword that does 100-200 dmg, so how do you get the rest of the way to 350?
Easy part, first, use your +100% alchemy clothes, and make a potion that increases enchanting by 25%, now use the potion and enchant your gauntlets, boots, neck, and ring to increase 1h weapon damage by 100%, now your sword that does 100-200 damage does will do 200-400 dmg(again, obviously youll need to use grand soul gems when enchanting).
with 20,40,60,80,100% perks in one handed, you can increase this damage even more, and if you get 25% power attack perk, and 50% dual wield power attack bonus you'll be killing dragons in one hit.....
There you are, the recipe for best sword in game.
btw, same trick can be used to upgrade dragonplate/scale armor to make you practically invincible too (ive got 1000+ armor rating with all heavy armor perks, and enchanted armor)