What in your opinion is the greatest nation on Earth?

Ahh, but he didn't ask us to name a "perfect" (without flaws) nation. Simply the "greatest" which is a much lower standard in an imperfect world. :)

But that's why it's impossible to assess, at least for me. Is the U.S., with folks getting shot every week and both billionaires and the highest homeless population living in the same city (mine) better than say, Sweden, with astronomical taxes and immigration problems ?

Ahh Bij! That speaks directly to my answer below. This question doesn't state the criteria upon which we are to make our decision. If the criteria is population, then certainly China is the greatest country on Earth! If the criteria is size of economy, then certainly the USA is the greatest country on the Earth.

BUT, (and this is what I love about you) if the criteria is social justice, then there is much about our country that leaves us wanting.

I wish "social justice" wasn't such an epithet nowadays. I admit, I don't judge a country's 'greatness' by size or wealth, but whether or not people can be happy, content and safe there. And I honestly don't know about other places besides what I've seen when I've visited and what the people have told me. Our country, imo, is in better shape then places with Sharia law or constant government coups, tribal infighting and disease. But it's not better than many other so-called "1st world" countries that invest in healthcare and education for their citizens and don't have constant problems with gun violence.

I think we're in agreement with everything you just said. :-)