Is Sanguine Rose the best weapon in Skyrim?
Best weapon? No.
The most useful weapon? Yes.
You don’t go around swinging Sanguine Rose onto the faces of your enemy. After all, it has 0 damage.
But you do summon a Dremora which makes short work of anything and anyone dare to glare at you (for 60 seconds). I found this to be a very useful skill to have in places where you cannot bring in your companion.
For some reason, it does not level up the Conjuration Perk, though.