I would say apply in the States, if you can afford the processing time (try travel agents or google for some). As a Singaporean, you're allowed 15 days visa free entrance to PRC, I believe. Beyond that you would wind up needing to apply for an extension while in China. Very very troublesome, need to show bank account with balance of USD100 for each day of extension, etc. Best to apply for a PRC 30 days visa before you go. Simple in SG or even simpler in HK via travel agents.