I'd favor Mayorga. Here's why. Breland didn't like to be crowded, he wasn't very good on the inside, and his ability to take punches was suspect... Mayorga beat a better clone of Breland in Vernon Forrest twice. Forrest also couldn't get a good grasp about how to handle the wild swinging crazy angles and pressure Mayorga put on him. Mayorga wasn't a great fighter, but before his crazy life style started taking its toll ( The smoking, drinking etc) he was as physical and tough as they come. Too tough for M.Breland.
I think Breland early yet Mayorga could come on late. Breland did have a nice right hand and he was a good fighter. Better than Mayorga.. sI don't think Vernon was a better clone of Breland. He didn't have the right hand of Breland.
Are you comparing amateur Breland or pro Breland? Breland as a pro had a good right hand. But nothing special. Trinidad landed titanic right hands cleanly, and had to depend on attrition to finally stop Mayorga, same with Mosley and Deloyhoya at Middleweight, where Mayorga was clearly not the same fighter he was at welter. All three were better punchers at the pro level than Breland.