Nine, ten, a big fat hen.
Here's a "what if" question for you. Ignoring for a minute that external forces are involved (that Doctor Who is written by people who probably would have written things the same no matter what), how would S2 be different if Nine never regenerated? How about if we had seen Ten already in S1?
Can you see actions being different in various situations? For example, would Ten have been nicer to Jackie from the start? Or would Nine be more or less freaked out about the mortgage conversation in "The Impossible Planet?"
Can you see actions being different in various situations? For example, would Ten have been nicer to Jackie from the start? Or would Nine be more or less freaked out about the mortgage conversation in "The Impossible Planet?"