While I did some more changes towards the end, I would also like to add that religion is a very opinionated subject and as such may be totally irrelevant to the question.
I understand what you're trying to say. And I agree with a lot of what you wrote. But on the other hand I think you seriously downplayed the Empires role (and we are discussing Empires here and not ethnic/religious groups) in the formation and spread of Christianity. Christianity is as Roman as apple pie is American (which btw is not an American invention, and because so is a fine analogy to what I'm trying to say, would you agree?
Regarding the original question, I voted for Rome because I believe it's legacy can be felt on a more widespread area then the legacy of Han China. But this could change in the future.