Ahhh the unanswerable question. Heard this discussion a few times over the years and it never gets resolved. I am a massive fan of Tyson so my heart will always go with him as i feel that at his absolute peak he was absolutely devastating, but having said that, i know that probably a massive percentage of his fights were won before his opponent entered the ring (just look at Brunos face) and this is where i think that Ali would come closer to beating him than anyone else as you just know he wouldn't be phased by Tyson at all and would go into the fight genuinely thinking he could deal with him. Having said this though, i still stick by Tyson but Ali would be a close second.