I'd say kabuto, Orochimaru was getting weak and on top of that Kabuto already knows Orochimaru from front and back. I mean do you really think Kabuto wouldn't be keeping tags of what's wrong with Orochimaru and what weaknesses he has?
It depends... if it is Oro vs Kabuto before Kabuto implanted Oro's cells than Orochimaru would have no problem at all. If we're talking about the new Kabuto the situation is very different.
If it was when Orochimaru was weak, well then its quite obvious. If you matched their powers when they both were actually fit to fight then Orochimaru of course.
I kinda am holding out for Kabuto to be Orochimaru like reincarnated. I mean he looks a lot like him, and I think it would be a bomb ass twist if Orochimaru had planned for it all along as was now in Kabuto's body.
The new and improved Kabuto versus a healthy non arm sealed Orochimaru....that fight is uneven. The skills and experience are too much on orochimaru's side. He'd be hittin Kabuto with jutsus he'd never seen before in his life! Just because Kabuto has Orochimaru's genes in him doesn't mean he knows everything that Orochimaru knew.