My Guess is probably Byrd. Most will pick Spinks, and in truth, he was the better fighter, but Chris spent far more time in this class..
I think Byrd was a better HW. Spinks did a great thing, but he still was not a true HW. Byrd would have been too slick. Have a baby by me and be a millionnaire.
Spinks he was the better fighter, was never defeated until Tyson and was the first man to beat Holmes who was a much slicker fighter than Byrd.