Would a black model be more succesful in Europe or Asia?

Europe is a lot friendlier for models of colour. There are very few black models in Asia. The foreign models tend to be pale skin blondes in Asia because the biggest selling sector in beauty products are whitening products.

Definitely Europe. anti-blackness is big in Asia.

In the country where (s)he is legal to work, has contacts and options.

If you have to ask, likely in neither.