All time I think that Alexis Arguello would have given Pacquiao hell because he was a tall fighter who knew how to box well from both the outside and inside. Right now I think the obvious choices could beat Manny at 140 such as PBF, Marquez, Cotto, but I think there is somebody else out there who can give Manny a helluva fight at that weight. Paulie Malignaggi he has fast hands, fast feet, and if sticks and moves, Manny would have a lot of trouble finding him. Manny does his best when guys come straight to him. The way to beat him is to never let him on the inside, use the jab and straight right hands, keep him at distance, and tie up if he gets too close. However, with that said ANYBODY who fights Manny at 140 is an underdog against him!!!!! But thats how I would train my fighter to fight him and those are some guys that I think could pull it off.