You guys are ridiculous. Fictional power-scaling should be judged by the character's best measurable feats, not speculation; and by feats alone Yamato edges out a win even over post-King Zoro.
First off, Zoro's best feat to date is fighting King, but he didn't even defeat King cleanly - it was a double KO draw with Zoro unconscious and within an inch of death. That means that Zoro ~= King (a Yonko Commander)
Yamato's best feat is holding Kaido (the single strongest fighter in the entire One Piece world up to this point) to a draw SOLO for probably a good 10-15 minutes. In contrast, Zoro could only barely keep up with Kaido in a 2 v 5 with 4 other extremely powerful fighters helping him.
By feats alone the win has to go to Yamato, until Zoro can do something equivalent.
"Objection! But what about Yamato's other fights with other randos before Kaido?" She was clearly holding back and not going all out, because she didn't even bother to use her hybrid zoan form until Kaido.
"Objection! Kaido was going easy on her in the fight!" There is no evidence to suggest that Kaido would care enough about Yamato, or anyone for that matter, to hold back even the slightest during a fight. He was clearly trying to kill her. Yamato held a Yonko to a draw by herself for 10-15 minutes.