I like the China Curtis Jenny over the Great wall on cover. The Stamp itself was engraved by Americans Lorenzo Hatch and William Grant. L.J.Hatch worked for the United States Bureau of Engraving and Printing as well as
the Western Banknote company and established the Chinese Bureau of Engraving and Printing on a 6 year contract with the Chinese Government. The Postal Museum has a wonderful Die Proof collection of the early works of these 2 Men, the "Junk" Stamp and the Beautiful "Temple of Heaven" were also designed by them.
A very good read on the story here.
http://postalmuseum.si.edu/resource...eproofs.html