In spoken language, people usually say "the United States" or "The U.S." rather than "the United States of America." "The United States" is the more common and casual way to refer to the country, while "the United States of America" is often used in formal or official contexts.

It depends on who is doing the talking and where they are. Foreigners often use ‘America’ formally and ‘The States’ informally. Possibly long time ex-pats use ‘The States’ too. In the U.S., we say ‘the U.S.’