Im using blade of woe and Mehrunes razor are there any daggers better than that?

Those are the two best daggers I've found so far, but I bet there could be others.

I use a enchanted Daedric Dagger, if that gives you any ideas.

i think the best daggers are the ones that you craft yourself with double enchantments , because not many unique daggers have a powerful enchantment , let alone 2 .

Blade of Woe is the highest dmg dagger before smithing . But if you max your smithing and use potions and smithing gear , you can upgrade other daggers to near the same dmg as Blade of Woe , the difference is negligible after improving it more than 300% , so at the end of the day , what makes the difference between daggers is the enchantment on it , and Blade of Woe 's enchantment is only 10pts health absorb ..

One of my favourite dagger is Valdr's Lucky dagger , i love it because the enchantment on it is unique (critical chance ) . Merhunes Razor is also very good , one of the best for the same reason , its unique enchantment has a chance to kill instantly , although it is very rare

I have yet to get an instant kill with Mehrune's Razor and I have been using it for almost 10 levels...

I insta-killed a dragon that still had half health... I think.
But my question is, is there a reason to use a dagger over a sword?

There's a perk that makes daggers do 15x damage when you perform a sneak attack. That's the only reason I can think of to use daggers.

That s because it is only a 1% chance to insta kill on this dagger , and since people who usually use daggers are Asssassin builds with the sneak backstab multiplier and DB gloves , most of the enemies get killed in one power hit anyway , so the bonus itself is not very useful for casual use , but against strong bosses if you get lucky , Merhunes Razor can be handy

I use the Blade of Woe. It has a better base damage then Mehrunes' Dagger. Im sure there are better though.

"Keening" is good. But I think you won't have it forever though.

The x30 sneak damage bonus (Db gloves + perk ) and if you dual wield , there is a speed bonus if you have a dagger in the left hand , which makes dual wield power attack much faster than with two swords

Daedric Dagger by far. Mine has 109 base damage, and with my Dragonplate set it almost pushes it over 200. I don't use it though, it just sits in my inv. looking pretty.

You can have Keening after Arniels Gane is done with the experiment. It's either on the ground or knocked out of the accessible ambient. But you definitely can pick it up. I have it.