ごとに, どの〜も, 毎 differences

Question

What is the difference between these three sentences, do they all mean "Every city is big in America." ?

アメリカはどの町も大きいです。

アメリカは町ごとに大きいです。

アメリカは毎町が大きいです。

Answer 1

Only the first sentence is natural.

The third one is probably understood but not idiomatic. [毎]{まい} is not such a productive prefix. It's only used with counter words for things that happen regularly such as 日, 週, 月, 年, and 回.

ごと (also written 毎) works more like each than every. After 町ごとに I would expect to hear something each town does on its own or some distinct characteristic each town possesses. For example, the following sentence sounds natural.

アメリカは州ごとに法律が違う。