I like Christopher Hitchin's reasoning that there probably was a real person that the Jesus story is based on because if it was being made up wholesale then the writer wouldn't have invented a census that can be proved not to have happened just to make a man who was known as Jesus of Nazareth somehow be born in Bethlehem.
If it was completely made up then you'd just have your man be from Bethlehem.
Also, the resurrection account is only attested to by women. If the story was completely made up then you wouldn't have the key event that proves that your man is more than a man verified by the least regarded members of society at the time.
This coupled with the fact that the rest of the story does fit into the mythological format that was widely used points (conclusively to me) to an actual historical person being fitted into a mythological story narrative.