For those who dont know:
Bruce practiced boxing too.
Bruce also won amature boxing tournaments in hong kong.
So i can easily say that bruce lee knows what he is going against. Thats one plus for him. cant say the same for boxers.
Physically speaking, he was incredibly far more tougher than m. ali and tyson for that matter. (might waana read up on the things he would do)
Far more agile than Ali.
Far more weapons than any boxer (two arms vs two arms and two legs)
And finally speed and power: mike tyson even in his dreams cant corner Lee. not a single boxer can avoid his punch as they were pretty fast.
punches were amazingly strong. and all the fight can just end in one strike. see the video below
http://pop.youtube.com/watch?v=gCph8rXsYj0Now the question the real question is, bruce was trained to take the punch any where and most importantly block the punch. None of the boxer are trained to intercepting block. so i guess tyson heavy punch will in the end go in vain and bruce lee's punch wont. Boxers simply cant block the kick and devastating power of bruce lee kick is very well documented.
But in the end all i can say is that this is another one of "who lands the first hit". Like many tank comparisons, we simply cant tag one type of fighter greater than other. Though in a street fight, all bruce lee has to do is kick boxers in the nuts and run. boxers could never catch up to him and will get tired :)
But then again god forbids if tyson or ali get a hand on lee first :)