Hi Wei item,
Thank you for your question.
In fact, it is hard to say which one is more popular. But there are two slight differences between them:
If you just agree with someone, you agree that something can be done a certain way, you can answer with “xíng.” If you quite agree with someone, you think something not only can be done, but is also a good idea, a good suggestion, you can answer with “hǎo.”
If you talk to your supervisor, using “hǎo” is more polite.
Wish your Chinese will get better and better.
July 29, 2011