私は米国人です vs 私はアメリカ人です

Question

They both mean I am an American but which is preferable in everyday speech and in writing, and why? Is the former more formal than the latter?

Answer 1

Today people never say 米国人 in everyday speech and even in written form most people express American as アメリカ人.

The obvious exception is on a newspaper. Writers there still express it as 米国人, for possibly two reasons:

1. 米国 is shorter than アメリカ.

2. Kanji is more suited than Katakana to vertical writing, which is still used in newspapers.

I also want to note that this tends to be applied to 英国/イギリス as well. Also, Kanji is often used to express each country (e.g. 仏, 独, or 伊 to express フランス, ドイツ, or イタリア) even on the web news just because those are shorter.

Answer 2

Honestly, I have almost always heard people from the United States use "アメリカ人". I think "米国"　can indeed be thought as more formal, and is used a lot when it comes to guidebooks and such. I see it a lot in writing, and when writing compounds:

• 米文学｛べいぶんがく｝: American literature. Any other form, 米国 or アメリカ, can be used there.
• 北米｛ほくべい｝: North America
• 米州｛べいしゅう｝： The Americas

Keep in mind that they both have exactly the same meaning: the United States of America.

• 米国{べいこく} comes from 亜米利加｛あめりか｝ which is I think simply a juxtaposition of Chinese characters to get the actual sound.
• Similarly, for France, フランス is always used in katakana except for French - Japanese dictionaries for which the chinese character 仏｛ふつ｝ is used. This one comes from 仏蘭西｛ふらんす｝. However, this only used when referring to "abstract" France, and never to refer to the country or to the people. You can also find it for example in the 仏検｛ふつけん｝, the French proficiency test for Japanese people.
• For the English language, 英｛えい｝ is used, but this one comes from England, 英国｛えいこく｝,　which itself is from 英吉利｛いぎりす｝.

So, they are the same but I tend to hear a lot more of "アメリカ" and see a lot of "米国" written. If you have a look on Wikipedia though, you can see most pages that have 米 in their name are redirected to their アメリカ counterparts which would seem to indicate that アメリカ would even be more correct or at least more frequent.