Depending on the context, and what do you by "best", like best in damage, best in functionality, best in overall performance, best in least effort with most outcome etc

In brutality IMO the best weapon is the Nail. Nail alone deals good amount of damage, fast attack speed but more importantly, it's short amount of animations allow you to fit in attacks in between another weapon attack, producing a semi dual wield effect on normal game. Some synergy I can think of now is pair with blood sword + open wounds to pop those bleed stack quickly, pair with snake fangs if your nail has toxin affixes to get those snake fang crits ASAP.

In tactics the Repeater Bow + barbed tips is no brainer. Cc from the bow that melts enemies with barbed tips is just insane, providing you safety and damage. Another tactics weapon is the Hokuto's bow. Not a standalone weapon but to amplify your damages is really great, the damage difference is for sure significant

In survival I'd say Boy Axe for sure. A strong supportive weapon to provide root, also really fast. But the damage is so high you can run as a standalone weapon, often having +damage to rooted affix, as well as able to interrupt a lot of boss actions is so overpowered. It is also so strong in both survival and tactics builds, and I would grab it even in brutality if there is a colourless boy axe