Is America The Greatest Country On Earth?

Clearly a presidential candidate has to strongly assert that America is the greatest country on Earth if he/she wants a shot at winning.

But, is America the greatest country on Earth? I'm not saying I think it is not, I just don't know if it is. I feel confident it is high on the list. Of course to take the question seriously you'd have to define what you mean by greatest. Do most people in America think America is the greatest country on Earth? Do all leaders of countries claim theirs is the greatest country on Earth (seems like there would be some countries where that would be too absurd for even a politician to say)? Do most people in other countries think their country is the greatest on Earth? What portion of people in other countries think America is the greatest country on Earth? What portion of people in other countries thought America was the greatest country on Earth 9 years ago? I'm not asking any of these questions to be rhetorical - I really have no idea what the answer is to any of them.

I realize a leader calling America the greatest country on Earth is in there with flag pins as a necessary but meaningless gesture (not that some leaders don't mean it, but since they all have to say it, you don't know what they really think). But I think it would be interesting to know what they really think. Because it seems like it would lead to very different foreign policies. If America is definitively the greatest country on Earth it would probably approach other countries differently than if it was a great country by reasonable measures, but not definitively the best.