Run every day as if a guy with a gun was coming for you....thats my advice....it builds up lung capability.
On sheer ability and head to head top 3-10 in history , personally I believe Liston at his best would be pure hell for any heavyweight in history not named Cassius Clay/ Muhammad Ali. And he beats about 98% percent including Atg's like Holmes , Marciano, Dempsey ,Foreman, Lewis, Tyson, Klitschko, and Holyfield. On what he actually accomplished top 15- 20.
He won against the linear champion in the most impressive style I have ever seen, he dominated very strong fighters like Clev Williams, Foley, Harris, Valdez, and for a while he was considered the best HW in history. In my opinion, the top 10 is absolutely ok. If he had withdrawn due to addictions after Patterson, he would have been in the top 5. But he did the same as Leon Spinks after Ali and Tyson after Holmes - he lost involvement. I rate him higher than others because he has reached a very high level.
It's always a hard one rating what could happen in head to heads etc, but for the sake of this rather wonderful thought experiment, we must be allowed the delicious luxury of rating the best version of the fighter we are discussing...and because of that, I have Sonny top 5. And before anyone asks, my other four are Ali, Louis, Johnson and Holmes...only Ali and Louis are guaranteed the top spots on any given day and the others move around in my illusory triumvirate on an almost daily basis. My 5-10 list changes all the time but usually includes Holyfield, who I sometimes swap our with Johnson in my top 5, Frazier, Foreman, Lewis and Bowe. Perhaps not a popular top 5 or 10, but for my sins, there it is...sometimes in the wee small hours I can put Tyson in my 5-10 replacing anyone except Evander. What of the Klitschkos..and Usyk...and Fury I hear you ask in my imagined fevered dreams...Well, any of them might beat any of the others but none of them male my top ten. Vitali might be the most compelling for me, but that's just on pure gut feeling. I await your brickbats and expect no bouquets...
On his capabilities at his best? Top 10 easily. Literally as a champion he wouldn't rate at all mainly because he didn't win the title until he was already declining. Moving to Las Vegas was good for Sonny in one sense but for his boxing career couldn't have picked a worse city. By February 1964 Sonny Liston was 87 years old in boxing terms. Drugs, women, the tables, the strip, not the best mix for Liston at that time.
Like Tyson after him, Liston does better in head-to-head than actual career accomplishments, but I only rank on the latter, as that’s concrete, not hypothetical. I see him as a back-end top 10 candidate most likely. He had a miserly championship reign, but did clean house dramatically & exceptionally prior to that. Eeerily like Tyson, in fact.