My first reaction was Whitaker right off the bat. And I know there are a TON of southpaws throughout history that won't get their deserved mention. But staying somewhat recent, it's hard to argue against Hagler. It would be similar to a judge scoring a fight between a Hagler style and a Whitaker style. Did you like the ring generalship complimented by speedy, accurate punching, extraordinary footwork and defense? Or were you more impressed by the aggressor who came forward the whole time landing the harder punches while forcing the fight? I personally think Whitaker was MUCH more skilled than Pacquiao ever will be. But how can you argue against Pacquiao when you factor in everything else? Personally, I give a lot of that credit to Freddie Roach, but that's a whole new argument.
Whitcaker faced youthful , bigger competiton on his way out. Calzaghe did the opposite. I figure actually mentioning Cal in this topic brings you closer to jackassedOM.
Hagler did not fight this way in the great majority of his fights. He used plenty of lateral movement and boxed effectively at range behind his long arms and great jab. Whitaker is my #1 southpaw of all-time, followed by Hagler.