A foreigner's perspective - I'd have to call the 1911. Why? For sheer longevity and breadth of military service all around the world, and which still retains significant popularity in the face of all the commercial alternatives. If any handgun best represents America and what it stands for, it is the 1911.
I agree with the SAA fans that their baby should get an honourable mention. And if you say the words ".44 Magnum", what is the first nation you look to on the map?