Re: Holmes (early 80s) vs. Ali (late 60s)
Ali is much quicker on his feet, and I don't particularly rate Holmes' footwork. He could cut off the ring when necessary, but he would find himself lashed time and again whenever he got Ali where he wanted him.
Although Holmes' jab was in my opinion his greatest offensive and defensive trait, Ali had little to no problem dancing around Liston's jab, and many rate that extremely highly.
I pick Ali by a pretty clear decision.