If Denmark and Greenland were to part ways and proximity was the measure of what other nation should “get” Greenland, Iceland and Canada would have stronger claims than the U.S. In fact, Russia would have a stronger claim than the U.S. According to geodatos.net, the shortest distance between main borders of Greenland and Russia (including major islands) is 956 km, whereas that distance between Greenland and the U.S. is 1,975 km.
But then, Russia and Iceland both fall under the category “Europe” and therefore, according to the Donroe Doctrine, must control no territory in the Americas and must exert no significant influence on Greenland, which is part of North America and in “our” hemisphere. That leaves Canada – “our” hemisphere belongs to Canadians, too – with the strongest claim to Greenland.
I almost forgot Norway! Since it’s in Europe I won’t bother to report all the ways of calculating distances, but among the European nations it wins on the shortest distance between main borders: 453 km. Even Sweden is closer to Greenland than the U.S.: 1,143 km.