Usyk from the toney Bellew fight is the best version of Usyk I've ever seen.

Do you mean at Cruiserweight or in general? I think the Usyk from the Dubois rematch is the best version I have seen; he basically fought Dubois at his own game and haymakered him into oblivion.

 

Usyk from Joshua 1 is the fastest and most agile version of him I've seen. After the final bell AJ was sitting on his stool almost collapsing from exhaustion due to the pace.

Usyk-Dubois 2 is the most clinical version.

 

It depends on how you classify his prime. The Dubois 2 knockout was punch-perfect, and he knocked out a HW champion in his prime who was a stone heavier than him. The Bellew fight was great, but I don't think it was his best performance; even at cruiserweight, his win against an undefeated Gassiev was the better win on paper: a 12-0 shutout in his own backyard to win the WBSS and become the first-ever 4-belt undisputed. I never used to rate that win as highly as I do now until I went back and watched the fight again; they were only a few months apart, though, so he wasn't that far off his CW peak.