Brook absolutely batters him, he’s a level above Margarito, he tattoos his face with the jab, measures him, controls the range, keeps him where he wants and therefore is able to read Margarito, measure him for right hands, lead left uppercuts, combinations, see everything coming in return and counter effectively with uppercuts, rights, bodyshots. Margito, with his earmuff guard and slower hands, would be a sitting duck for the brilliant punch selection of Brook. This would be a beating.
I'm still not convinced Margarito was totally legit. He was on a run of stopping fighters prior to being exposed in the Mosley fight with the handwraps. After Margarito got exposed he had 0 stoppage wins for the rest of his career. So based on me having an asterisk over Margarito I'll pick Brook.