Mayweather is better than Marquez, but will do much worst against Pacquaio.

Technical summary Mayweather is obviously the superior fighter to Marquez. I don't think anyone should be debating that. What people do need to understand is that Mayweather is a fantastic counter puncher defensive fighter that people mistakenly link to Marquez's own counter punching style. They are totally different and one style have always caused Pacquiao trouble, the other will not. They are completely different fighters who set up their counters completely differently. First off, the key for Marquez against Pacquiao has always been his constant lateral movement. Not only does he constantly sway at a low center of gravity while rotating away from Pac's left, but he pivots out of range and changes the angle after landing an attack, or even in the middle of an exchange, to completely confuse Pacquiao and take away his ability to take the initiative with his amazingly swift footwork. He does this so much so that in the second half of the fight, he caught Pacquiao with a left hook pretty much behind the head because of how he was able to laterally shift away from an oncoming Manny. Mayweather on the other hand is a more conventional "slick" counter-puncher who relies on his control of distance to anticipate and neutralize his opponent. While he's brilliant in reading his opponent and measuring his own punches against their own, he usually does this either going straight backwards or straight forwards, with efficient footwork. He has habituated himself to fighting in straight lines in order to land his favorite punches; lead right hands, pull-counters, jabs to the body, counter or lead left hooks, or counter-right uppercuts when swarmed. But one thing Mayweather almost never shows is the type of lateral movement Marquez shows. De La Hoya, while still game, had an offensive gameplan that relied a lot on mere feints and swarms of activity to back Floyd up, and he usually did so with no problem. Even after Mayweather adjusted to his rhythm and started winning rounds, he hardly ever looked impressive and was backing up consistently without ever shifting towards a laterally-minded gameplan. Wouldn't that have made things easier for him instead of constantly giving up the center and having to retreat to the ropes to counter before escaping? Someone with the style of Hopkins (as in VS Pavlik), for example, would prefer such tactics, and Floyd seems to prefer seeing his opponent right in front of him, positioning himself right in front. This comfort zone does not appear to be a preferred strategy for someone who can rotate so quickly and match Floyd speed for speed with plenty of pop behind it.(Manny) This leads into my second point, which is that Marquez's movement allows him to get Pacquiao on the inside and punish him. As an in-the-pocket counter-puncher, Marquez can duck under and find himself body-to-body with pacquiao and take advantage of his unpolished inside game. Uppercuts, combinations, and even spots of controlled aggression (before pivoting out) are something that he can do because of his relatively similar size to Pacquiao. Now, while people point to Mayweather's reach giving Pacquiao issues, I don't believe he'll be able to use it to control Pacquiao if he shows his regular movement. Floyd's accurate and reflexive, but his defensive stance by nature anchors his back foot to the canvas, and allows someone as fleet-footed as Pacquiao to change the punching angle and capitalize for an offensive opportunity. Fighting in straight lines is not the way to beat Pacquiao; you have to take away the punching angle, and I don't think at all that Floyd can circle as well as he can back-pedal. On top of all of this is tempo. While Marquez was able to control pace from time to time, he was still able to fluidly exchange with Pacquiao and see the angles in order to time the better shots while rolling with Pac's own. Mayweather, as skilled and tough and intuitive as he is, has not shown this quality in abundance. The times he's been hurt actually, have been times he's over-committed to his own punches (Corely, Judah, Mosley). He can adjust brilliantly round-to-round, but as controversial as it may sound, I feel he lacks this sort of intangible fluidity Marquez has in his approach. Once again Floyd is the superior fighter to Marquez but he lack the particular attributes that Marquez have in the counter punching game that have so enabled Marquez to be Manny's biggest nightmare.