Probably depends on the rule set. Modern ring, Modern gloves, 12 rounds I'd back Spinks for sure, even though I don't think he holds the best victory between the two.
Depends on the Leon. 1978 Leon pulls a Dempsey-lite like performance. KO5. Later coke-addled Leon gets torn apart.
If the Leon who ko'd 6'4 230lb power puncher Bernardo Mercado shows up then I pick Leon. Other than that Willard.
Willard holds and maul's spinks though Leon may rock him occasions .This pattern continues through out the fight .If it's a 15 rounds then spinks might just Nick it on points. If it's a long distance ,then Willard eventually stop's a fatigued Leon gasping for breath ,around the 20 th.
Why would the longer distance favour Willard? Looking at their physiques, Spinks looked in far better condition and looked like he would last longer at a fast pace than Willard.
Because we know Willard could go 20rds plus in heat and win? Any time Jess wanted a rest he would just tie up the smaller man.
Exactly this ..spinks could pummel away all he wanted but Willard would just grab him and clinch .By the time the fight s nearing the 20mark ,Leon s used up that much energy punching and trying to get out of Willard s clinches ,that he'd be drained. Willard on the other hand would still be as strong.