Who do you think had better defense Roy Jones Jr or Mike Tyson?

Tyson. No question. Tyson has the most underrated defense in the modern era. Find on youtube tyson defense video's, he was a master. The best thing about Tyson's defense was that he was set up to counterpunch as he avoided punches.

RJJ's best defense was offense and hand speed and his defense was his use of his superior reflexes.

Tyson. His defense, consisting of that signature head movement, might've been underrated but it allowed Mike to get inside his opponents, especially the taller ones, then blast them to pieces with devastating combinations. Jones has no defense. He's an offensive fighter and he simply overwhelms the opposition with his fast and powerful hands. But as soon as he aged and became slower, he got KO'd quite a lot.

Mike Tyson's defense looks like proper boxing defense(bobbing and weaving,slipping) while RJJ's defense was more about his superior athleticism. RJJ could avoid punches, yes, but it was more of the "swing head out of way variety" rather than proper slipping of punches. When his athleticism left him as he got older, RJJ got hit much more easily, while the type of defense Tyson used could be used effectively by even an old fighter who isn't even that fast. Look at Archie Moore, a fighter with similar defense to Mike Tyson, fighting into his fifties and still hard to hit thanks to his skilled,proper head movement.

tl;dr Mike Tyson's defense comes from understanding of boxing fundamentals, RJJ's defense came from being naturally faster than everybody, and left when old age crippled his body.

Tyson, at least pre-Douglass Tyson.Like Bundini said, the head movement allowed him to get inside.Roy basically allowed his reflexes to defense him, also like bundini said, once they were gone, he was caught.