By rule of hierarchy BM>King. Zoro was unable to turn his blades into black because he never fought a yonko in 1v1 alone. I mean black blade results from long usage of haki and high intensity fights. King by no means a weak opponent hence a good stepping stone for Zoro.
Kid made someone as tough and big as Mama fly away by gripping her with his metal arm.
With his opponent turning into magnet he could ragdoll them as much as he wants since metallic stuff will be stuck on them.
I voted Sanji's one in the poll because it's the most justified PU among them all. Oda made an entire saga to arrive here with this Wolverine-like Sanji.
Most powerful one is obs Luffy's one.
Awakenings are dope, while I just don't care much about Zoro and Enma because it's essentially a pretty generic magic sword from an rpg and I preferred Shisui and the legend behind that blade, but it's a good PU as well I guess.