Congratulate for your funded acceptance! Although Duke is smaller in terms of size, I think the quality of your graduate life depends even more on fit, that is, the fit of your academic interest toward Duke/Stanford and their faculty. Both of them have great faculty on Chinese politics/sociology, while their relative strength of sub-areas differ, such as democracy of China, social protest, comparative politics, etc. As for social science as a whole, you should take your research further. Just my two cents of thought. Please share more student contact results, I am actually considering between several of these schools too.
By the way, what's your reason to choose Stanford over Harvard? I'm now quite hesitate for asking Stanford on funding issues(I didn't contact any POI prior to application).