.us is fools gold.
we have all made mistakes, especially in the beginning. You will learn pretty quick that .us is not popular at all. Can you think of one or two popular sites that actually use .us?
.us is a trick, It can be confusing to new domain buyers because .us should make sense, but once you realize the USA is king of the world as far as economies go, and .com is king of the internet, it only makes sense that the USA would use the king... .com.
However other country codes like .ca (canada) .de (german) or .uk (united kingdom) etc are actually used in those countries(for culture, language, reverence, Local, etc). However, these counties are interested in the USA because of Trends, TV, Music, Celebrities, Political, Technology, Large Economy, etc. So they visit the 'main stream' which is .com not .us
Cheers!