IMHO you should never buy your currency in the US as you are just asking for a bad trade. My experience in China is that the government regulates the currency exchange so you shouldn't get ripped off. However, in for instance Hong Kong the hotel exchange rates are generally terrible and you are much better off at a currency exchange. If you have an atm card that does not have service charges or Bank of America and use one of their partners atms ( China Construction bank in mainland) then you will get to within 3% or so of the published exchange rate which is pretty good.