What is the richest country in the world?
It depends on how you measure 'richest' - it's not easy, because simply taking average income per person (income/capita) won't always be accurate, especially if it is distributed very unevenly.
Another problem is that 'wealth' isn't necessarly reflected in moneytary income - not only do people produce much of their own food in some countries (and thus don't need to use cash so much), some countries - Bhutan is a prime example - have emphasized 'Gross National Happiness' instead of Gross National Product (GNP).
The UNDP has developed a Human Development Index that measures not only income but also things like education, health standard, human rights - you could look at hdr.undp.org/en/statistics or
the list at en.wikipedia.org/wiki/List_of_countries_by_Human_Development_Index
In recent years, the Scandinavian countries have tended to score at the top, with some minor variations. No, the USA does not head the list.
right now? Who the hell knows for sure.