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I use Korbit. There are currently three major Korean exchanges which provide open API: Korbit, Coinone and Bithumb. Korbit is the most stable among these three, I believe.

Would you recommend me any trading platform I can use in US?

I am not quite sure which exchanges are usable in the United States, but as a rule of thumb, it pays to use the most liquid exchanges(high volume). You can find these data on www.coinmarketcap.com.