American Traveling to China

I am an American tourist planning to do an Asia Trip. I will be traveling to China for 1 week from Thailand. If I apply at the DC office which visa should I apply for and how long does it typically take? Will they be able to email me a visa letter or will I have to have a hard copy at the airport? Will be leaving in approx 2 weeks for my Asia trip, however China is my last country on this 5 week trip.