for some reason:
*When they were partners in Akatsuki, Sasori was the SENIOR and Oro was the JUNIOR
*Oro needed Kabuto to prepare an ambush when they were meeting "Sasori" in the bridge
*Sasori said that if he had the chance he would kill oro. (don't remember where, but it was stated.)
Sasori wins this.
1. back then, oro didn't have all of his research and techs like he does now. so it's highly probable that sasori knows nothing of oro's rebirth and whatnot.
2. oro didn't need kabuto to kill sasori. it's called stragety. oro knew sasori thought that kabuto was still under his mind control shit. so it's very logical for oro to send kabuto there.
3. again, sasori knows nothing of oro's new techs since he was in akatsuki. therefore, those are words spoken of an ignorant man
all in all, orochimaru wins this. ppl say poison will be a factor, but look how long it took for chiyo and sakura to even be hit by the poison. so my bet is on oro...