Has there ever really been a greater PRESSURE fighter than Iron Mike? And if so, let's see your references.:yikes
Among the names already mentioned . . . I'll pick Tyson over the rest because he is the kind of fighter who won't stop punching (in his prime of course) Duran and Frazier are very good candidates but I've seen them on the defensive more . . . than I've seen Tyson.
Two versions of Tyson. Iron Mike was not as good as Fraizer. Kid Dynamite on the other hand was better.
Many, many more fighters. "Pressure" is overrated. You could weather Tyson's pressure. Frazier, Holmes, Lennox, Ali, Holyfield, etc... you couldn't. They would keep coming and coming with jabs or hooks or whatever their game was for the complete 12 rounds...