Max Baer deserves some consideration. In 84 fights he was stopped for the count only once, against the great Joe Louis. And he was completely conscious. Baer had an iron chin.
You have to be fair that Martin and Ali were when we was well washed up. His fights against Clevland Williams and Zora Foley alone qualify him.
What about this guy he fought a lot of big hitters throughout his career and never failed to see it through to the final bell? He didn't even turn pro till he was 32 and didn't hang up his gloves untill he was past 50. http://boxrec.com/boxer/4537
McCall sparred 300+ rounds with Tyson and never hit the canvas. Bruno was a savage puncher and he went the distance with him. He ate all of Lewis' right hands like they were nothing. Vitali's chin is overrated imo. He didn't get hit much for the most part and didn't fight many quality punchers.
90% of the ATG HW boxers were American, so its actually an accurate representation of the sample. Its YOU who is being biased, by falsely claiming its biased for your own agenda.