It has the potential to be the best, certainly the most powerful nation by far. But I guarantee you though that America is not the happiest nation. America can improve in many areas. However we do educate the most people and have more freedoms than most.
I always hate the anti american sentiments though. My ex gf moved to Germany for college this past year. She always poo talked America even before she left. She was an ungrateful slut though, always thought the grass was greener on the other side.
Australia seems like it would be top 5 to me though. It seems like America with less hassle and more beaches.
Australia would be ok. Personally, I don't think most of the European countries have enough diversity to be the best. But to each his own.