Basically Hagler`s reach was 75, Nunn`s 77, Ali`s 78 and Bowe`s 81, Bowe`s jab would bother Ali more than Nun`s jab would bother Hagler because of the reach advantage, Ali never faced a jab like that apart from Hlomes`s when he had parkinson`s, Nunn exploited his reach and speed, Hagler`s jab would nulify that. Ali was a better fighter than Bowe though, just saying the gap between Nunn and Hagler was bigger, Nunn never beat a fighter as good as Hearns nor did he beat a fighter as good as Holy.
Either could happen, for me. But I'll go Nunn beating Hagler. That's certainly not out of the question.
If Nunn stepped into the ring in April 87 instead of his Sweetness, I think Nunn might even won via a blood stoppage, but certainly by decision, with little if any doubt to it. I know Nunn was at least a year off hitting his peak, but 87 Nunn had the tools to beat 87 Hagler. He hit hard enough when needed to get Hagler's respect, and his speed and awkwardness would befuddle the Marvelous One at times. But the Hagler from 77 to 85 will always beat any Middleweight version of Nunn.
