Imo, Madara still stomps here. EMS is just too overpowered when we're talking about the Antichrist of Naruto who is also the guy that literally can go toe-to-toe with the first Hokage, while Orochimaru had trouble with the seventh as a teen.
If Oro has a body that has Hashirama cells and Madara or Sasuke cells.. plus he has an Uchiha body which awakens the Rinnegan because of it.. give all of Oro's knowledge abilities, and techs in his arsenal to that. Then I would say that Madara cannot and will not win in the end. If Oro has his own Susanoo/CB Susanoo from this Uchiha body he took then it makes it even more apparent that Oro will kill Madara.
Now before my whole paragraph above, I need to know.. does Obito have both his original eyes? Thus having his Susanoo?
All my bets on Orochimaru. By the time Obito lost the Tailed Beasts, he was a Juubi Jin. Also by that time, Orochimaru was already restored to normal and had restored his arms. So, Orochimaru not only has the body of a Juubi Jin and Six Paths Chakra, but Sakon and Ukon's KG, Shikotsumyaku, Jugo's Clan's KG, and Wood Release.
Just imagine the stuff he could pull off with that kind of combined power.