as in oblivion you had umbra, which no matter your levels or gear it would always be better than every other weapon even daedric, except maybe shadowrend, so is there an umbra like weapon in this game? a weapon more powerful than all daedric weapons etc? or is daedric the best were getting?

Considering how much smithing can boost your weapon, I guess no.

Best weapon can only be crafted and enchanted.

So far the Skyforge steel sword.

i have 100 in both of those things, and actually you can upgrade unique weapons i have several times, for instance mehrunes razor the daedric artifact i have upgraded, same with dragon priest masks and other unique armor/ weapons

Yes Veveks sword always levels with you if you dont give it to the blacksmith.

Last time I checked you could upgrade unique weapons. So the way I see it, if they have a higher base damage and unique enchants, they can still be better than generic crafted weapons.

Wuuthrad is the best so far. 61 (or 69 can't remember) damage. (w/ all ranks of the Barbarian perk)
And I enchanted it with 20 Fire Damage.......used the only Grand Soul Gem I had.

i done some looking up, on a wiki, and it was just the base damage non upgradable so the highest base damage will be the highest normal damage once upgraded to legendary.
the daedric sword base is 14, and there is a weapon called "giant club" with base damage of 60. if that's the truth then that upgraded will be insanely powerful, if a base damage daedric sword if 14, and i have mine upgraded to about 73 damage, then starting at 60 will go way way up into the hundreds. but it could be the weapon a giant uses and non obtainable with a console command.
but a weapon called "nightingale blade" seems to have a higher base damage as well.

http://imageshack.us/f/88/2011111400010.jpg/ is the most powerful weapon i got currently. even if others have more damage... this is the best.. just slash away at your enemy and they will eventually go from 90% hp to 0% hp in one single hit
did most dragon slaying with this beauty

yep i have mehrunes razor and i use it alot for dragons too, the dragons usually get to about half hp every time before they drop dead, it's not super useful against like alot of enemies in a cave though, because your not hitting every guy like 400 times like you will a dragon, so chances are you won't get the insta kill, it's best used against dragons and bosses and people with tons of hp so you can swing crazy amounts really fast and the chance for insta kill comes better.
daedric weapons are better for caves though they just take lots of life and no worry bout getting lucky.