Obito when he was a kid cannot even keep up with kid Gai's speed and we all know VotE Sasuke is as fast if not faster than Rock Lee in base so he just blitzes.
If it's Obito before he got crushed by a rock, then Sasuke stomps him. If this is Obito who murdered several Jonin and Anbu with ease, we all know the answer.
If you mean the Obito who saved Kakashi when he unlocked the Sharingan then I think it could go either way. Sasuke beats kid Obito without Sharingan and loses to the Obito that Madara saved him.