I personally say Mike for both. Better, deeper resume than Pryor and a better fighter with a higher peak, but I'm sure they'll be many saying Pryor.
Both have beaten two ATG's. Pryor beat Cervantes at the end of his career but still a good win, Arguello above his best weightclass and a bit past his prime also a huge asterisk over the win. Tyson beat Spinks who was above his best weightclass but still good win, Holmes who was considerably past his prime but no asterisk in the manner of victory. For me it's clearly Tyson he has more filler to his resume and better names overall, their two best wins are comparable in some respect. But for me Pryor's win over Arguello as i said has a huge asterisk over it because of the "black bottle" i don't consider it a legit win. Pryor also didn't have a successful comeback when he took his first loss, atleast Tyson had some success after his first loss to Douglas and comeback after his prison stint winning a title.
Mike Tyson clearly. Love Aaron Pryor but I think many would say that his overall career is lacking and didn't get to face the best fighters enough. His drug problems definitely halted his career and wasn't able to make a comeback successfully whereas Tyson was able to bounce back. Plus the bottle incident against Arguello, despite that being an official win, is something that will always be a black mark to his resume.
Spinks did more at heavyweight than Arguello ever did at junior welter. And as an earlier poster said, Mike didn't need a special bottle to blow out Spinks. Also, Holmes had more left in the tank than Cervantes had. Moreover, as was previously stated, Mike's resume is much deeper when you take away both beating aged HOFmers.
Tyson. The Tyson revisionism where he isn't one of the greatest champs ever is really starting to **** me off. Sure, he had a short-ish prime, but so did Dempsey, Marciano, Frazier... and he fought elites competition for 4 straight years. Meanwhile, some stumblebum from the early 1900's will be given overstated credit for beating up wharfbrawlers and beet farmers.