I'd say Roy overall, since often "most vicious" and fastest would suggest a different approach. He's one of the rare guys who could basically shoeshine and throw flurries while making some of them concussive punches. Meldrick Taylor probably threw in bunches with as much speed as anyone you could find, but there weren't single shots in there that were that deadly. Someone like Marquez on the other hand wasn't especially fast at all but put punches together in order to set up one or two really damaging shots and could follow up on them as he was set to punch with power, same time he was sometimes caught hard in the process by faster guys.

Roman Gonzales is another very good example of a modern guy who can really mix it up with speed and power in combination.