I think Dawson and Berto give PAc a run for his money but I pick Pac cuz his feet move as fast as his hands.
He doesn't sit down on his punches, he mainly throws arm punches and every now and then he'll sit down on them just to make the opponent think about them. Whereas Pac puts a lot into all of his.
I think Berto has the fastest hands just now, Pacquiao 2nd. Calzaghe's hands are quite fast too, but it's very easy to look like a blinding flurry when the punches have no weight behind them, so he finds himself some way down the list for that.
Another example of how quick Pac hands: Animated Gif #1: Manny Pacquiao's "put on the brake" punch This content is protected Animated Gif #2: Straight Power Punch Left before a left jab This content is protected