based on hype and and the way people in the ninja world speak of them in term of power. oro was suposed to become the hokage that means hiruzen preferred him over the other sanin that makes me tend to think oro is stronger than them.
also because of 8 branches jutsu and formation of ten thousand snakes each o whom can remove a aword of kusangi from their mouth which would be a problem for kisame. the hardest things in the narutoverse are juubi skin, kyuubi skin, adamantine staff, kakazu's skin while using earth spear and then kusangi.
not only that oro s fast a genius and proficient in taijutsu and lets not forget his giant snake summons as well. also his mud clone can reform itself i think the only way to beat is fire or lightning style neither of which kisame has. he can can use the jutsu that was allowing to take tsunade's punches without harm against kisame.
so overall i say oro simply because everyone in the narutoverse especially the hidden leaf make him sound stronger than kisame so i hope you're not mad but ost of my answer is based on hype cause we haven't seen a REAL oro fight
