Comparison is hard, because states themselves are the size (land and population) as other countries. People that would be counted "immigrants" elsewhere are not.
E.g. Switzerland has an unusually high immigrant population, but also an unusually high emmigrant population.
The U.S. has 52m immigrants and 4.8m emmigrants. [1] Nowhere else is nearly that ratio. Next closest would be Canada.
It's nowhere the top as a percent of the total population. It's at the top in absolute number because it's the largest developed country by far.