Actually, volunteering is first important to your personal growth. People with public sense are, of course, more appreciated by top b-schools who are seeking well-rounded potential business leaders. So it is wise for our Chinese professionals to get involved in such acctivities or join related associations.
I don't think there is one kind of activity that would help you in your application. Find something you're truly passionate about and would enjoy doing (remember you're not getting paid!).
From my own experience, having the community service/volunteer activities has been great. It truly opens my eyes to things I otherwise wouldn't have known. I won't do it just for the sake of applying. I don't know how much it helped me get in b-schools. It might just have been extra icing on the cake. Other parts of your file must come through first. Also, AdComs are very good at noticing the intentions of your activities. If you have done nothing in the past, only started volunteering several months before applying, it looks suspicious. However, having something is still better than nothing.
