What is the most widely used shipping company in the United States of America?
most widely used refers to max(count(ShipVia)); shipping company refers to CompanyName; in the United States of America refers to ShipCountry = 'USA'
SELECT T2.CompanyName FROM Orders AS T1 INNER JOIN Shippers AS T2 ON T1.ShipVia = T2.ShipperID WHERE T1.ShipCountry = 'USA' GROUP BY T2.CompanyName ORDER BY COUNT(T2.CompanyName) DESC LIMIT 1