Well that settles it then, the greatest nation on Earth is undoubtedly Greece. Good work. Greece, you are hereby proclaimed the acme of world civilization.
The thing is, there are two contrary definitions of greatness. One is "kicking ass," by which the US is the only player in the game; other attempts to play just demonstrate the lack of competition. The other is "nice place to live." Anywhere can be argued for that. With the second definition, you are almost always looking for smaller, less significant places, because the reality is that even a small neighborhood which is affluent will be far "greater" than the mightiest nation on Earth -- if your definition focuses on social services for its residents. Basically, three blocks of Brentwood, where I live, are far "greater" than any nation on Earth by those criteria.