I'd probably say blowing Lounghran out of there in three. Very, very few men did that in a career that spanned almost 200 fights. John Conteh.
He never truly did himself justice once he won the title, but going to Denmark and beating the forever unlucky Yaqui Lopez was Conteh's best win IMO. Keep going with 70s 175lbers... Matthew Saad Muhammad (Franklin)
Tom Sharkey's best moment in his career came against Jim Jeffries in what was an epic. give and take struggle, from what I have read about it. Try Willie Pastrano.
Rex Layne had seen better days so I say his best win was to snap Harold Johnson's seven year unbeaten run. Ray Robinson...
Conteh was completely shot by the time of the rematch. He hadn't much left in their first encounter, while Saad was at his peak. And the decision was disputed (hence the rematch). John of 1974 beats 1979 Saad easy.