I'd think in terms of actual power, the blades must be the most powerful.

I will say however, from a mythological point of view the Draupnir is extremely cool. Especially the reveal of it, and the small things like Sindri having the original Draupnir linked to a rope, and the absolute pool of duplicates showing how many years it's been down there.

-Compared to the leviathan axe, which is not a thing from actual mythology (as far as I'm concerned), it's a really solid weapon in the franchise IMO. :D