If he was British, then obviously HK.
But if he was Chinese, it would depend on his beliefs and abilities.
In post-WWII Hong Kong, he would be a second class citizen in his own homeland. Barred from the highest levels because he wasn't British and have to live through "Jim Crow"-like social rules.
In post-WWII China, he would be living in third world conditions and having to navigate the Cultural Revolution.
So the question is what his beliefs are and how much ability he has. In China, he could at least raise up the ranks and won't be discriminated against because of his skin color. In Hong Kong, he wouldn't starve, but he and his descendants will suffer through colonial mentality.
Personally, if I was Chinese, I would take my chances in China.
By an incredible margin--10 to 1? 100 to 1?--Chinese people chose to migrate to Hong Kong from China, not to China from Hong Kong.
You'd have to figure out some way to normalize by population, but even then, the point stands.
Or if we are to play realpolitik without a notion of human decency: by Thatcher's time the Chinese had every local military advantage. The Brits were forced to concede a losing position and should count themselves lucky that the negotiations resolved peacefully.
The hubris of the Western colonial view never ceases to amaze.