I don’t know if there is uncommon boss weapons, but let’s just stick to weapons that don’t drop from bosses/minibosses. I love the Greenwich Staff (?) weapon, the grab attack is fairly good, and its E ability is very useful for me.
Personally, the dual swords & rapiers are my favorite common weapons. Dual swords Twin Crescents & Sword Draw: Mirrored River are very fun, useful, and make use of a fairly decent range. Additionally, rapiers have Shining Cycle, which is great for combos against players and bosses, or large hordes of enemies.
Honorable mention to the claws for good close range attacks, and Beast Instinct mauling lower level enemies (plus time to think)