If you check in the dedicated server offerings section, you'll find that a lot of the hosts will list a test ip and file you can run a traceroute to see, as well as try and see what their speedtest file results in. My guess would be that something on the west coast of the us would result in lower latency, and higher speeds.
Since you are located in Vietnam, I would recommend something located on the west coast of the United States. Take a look at Seattle and or Los Angeles. WebNX and or Pacific Rack are good choices. Best of Luck on your search!
I am from Vietnam. Now I am looking for a dedicated server provider in USA that has a good connection to Vietnam. What is the recommendation?
Can you list more details of your requirements pls? In Vietnam, there are some vendors provide servers in the US, have you checked them out? Even not all of them are equal, it's easier for you to make payment, especially if you need VAT invoice