I think if this was Broner now vs Cotto when he was a welterweight, I would lean to Cotto. Malignaggi landed 25% acording to showstats or what ever Showtime calls their punch count tracker. 25% is by no means world class defense. I think Cotto is a bit overrated and those punch tracking services are not 100% acurate. It still shows that he was getting hit. Cotto hits harder than Malignaggi dose. I think Cotto would give The Problem, a lot of problems.
There is no comparison between Broner and Mayweather.... Broner is there to be hit, and the key to defeating Broner is to walk him down. If you let Broner walk you down, you loose... At this stage... Brother needs to stay from Maidana, Garcia, Matthysse, Cotto.... Because they will come forward and as Mayweather himself said, Broner is flat footed.
Cotto is clearly on his way out; however, if he were to move down to welter and fight Broner, he would tear him to pieces. Classic welterweight Cotto (pre-Margarito) would literally kill him in the ring. Broner isn't on Cotto's level.
It would be easy work; Broner would get a VERY sizable paycheque for three rounds of work. However, he would have to recover from a somewhat serious concussion...