I choose the original Uchiha brothers Madara and Izuna. Now with Izuna alive both have their MS but with Itachi alive the only one out of the pair to have MS is Itachi seeing as Sasuke gained his through killing Itachi (and realizing the truth and unlocking it through his pain). So it's basically
MS vs MS
MS vs Standard. I'm not basing my argument completly on that however Madara and Izuna were rivals as well as brothers and they went toe to toe also I just believe that if we saw Izuna's skills we'd be able to compare him to Madara even now. I stick by my decision.