Could you put more info in this battle?
I voted for Orochimaru. Deidara is ass against anyone with range and Orochimaru has that sword that can stretch hundreds of feet. Despite Deidara's ability to fly, he's got pretty terrible mobility as evidenced by his inability to dodge Kakshi's slow MS attack and Sasuke's sword and shuriken attacks, all of which were launched while Deidara was airborne and his opponents were grounded. Without that, all he has is the suicide bomb. When Orochimaru was half-dead and his body was rejecting him, he was able to stand up to a close range bijuu bomb attack from 4-tailed Kyuubi Naruto and other moves that turned a massive forest area into little more than a crater in the ground by using jutsu and other techniques/skill. If he's a full health, I definitely think he'll be able to survive a suicide attack, making him the victor by default.