Vitali followed by Roy Jones Vitali has the best reflexes P4P, his defensive wizardry was based purely on reflexes fighting effectively with a hands-down stance is much more difficult when you're a 7ft behemoth
yeah this is a basic test for measuring reflex's and usually shows everyone to have pretty much the same
cant really be measured .... reacting to what ? in terms of reflex's everyone has pretty much the same reflex speed (barring any mental disabilities)
Besides those that were mentioned I think Mark Too Sharp Johnson deserves a shout. Although he was mostly an offensive fighter he could fight like Sweet Pea at times. https://m.youtube.com/watch?v=WJIS59oXx2E
First name I thought about. Dude had crazy reflexes. I'd also like to say Naz had great reflexes. If you want to go old timers, Willie Pep I would think should be mentioned. Without saying the other names mentioned already are great as well: RJJ, Whitaker, Mayweather, etc.
Floyd has better defense, but RJJ'S reflexes were incredible. Watch him in his prime react to punches coming at him abd how quick he was to exploit instant openings. Floyd has better technique and a type of sixth sense imo. He knew what you were going to throw