Noone.
Buster, Evander and Lenox didn't fight Tyson with speed. From 88 it's different story, he wasn't boxer anymore but brawler. Strength before speed, different training, motivation, Lifestyle, everything. These guys that won against him were not even close to him in his prime and don't forget with proper training he would improve even more. D'Amato's and Rooney's Tyson was the best boxer ever and he could become even better! Speed, stamina, movement, headmovement, punching power, intimidation, everything!
Such a pitty cause his head wasn't on right place. He needed a mentor and guidance all the time and than he was like invincible pit bull, without mentor he was just another fighter.