With something like this, you have to stay away from celebrities. It has to be a thing where you look at the bulk of the citizens and make a call based on how the public looks. So you are right that the USA is way, way down on the list of good-looking people. Go to any public square in the USA or Great Britain: bus stop, airport, etc. Everyone looks awful.
I'd say average good looks might go to a Persian country. I am always surprised at how attractive the Aussies are, but aren't they just Brits who colonized Oceania?