No gimmicks such as Zetsu clones, No Edo Tensei, just the two of them. Kabuto is in his strongest state, whilst Obito will be compared in his weakest state to his strongest (Kid Obito, Orange-Mask Obito, White-Mask Obito without Jinchuriki, White-Mask Obito with Jinchuriki, Juubito).
Kid Obito doesn't have access to the nine-tails power. IMO, I don't think it should be considered as part of his arsenal, as he gained it in the same battle that he lost it. Also, his control of it is not like Madara's control of it; he cannot summon it at will at any given time. It's like saying Pain has control of the nine tails, because he managed to hold it in Chibaku Tensei for like 10 minutes ->> Not the best example, but the point stands.
Three Arenas: Ryuchi Cave - Kabuto's Advantage
Destroyed Konoha - Level playing field
Uchiha Hideout - Slight Advantage to Obito (Couldn't think of anything better).