Only reason he was able to surpass Orochimaru was his cells, if it wasn't for that he wouldn't be relevant. He used Orochimaru studies to get that far. Orochimaru had years of research, Kabuto just added on. Orochimaru took Kabuto's knowledge added on to his own. So he's smarter(IMO).He surpassed Oro in every way , he did & perfected everything Oro couldn't do .
To me Kabuto is smarter <------------------------------- To me tho . Bro , To me .