A project begun in 1995 by the Russian emigrant artist team Vitaly Komar and Alex Melamid identified the most wanted and least wanted paintings on the web.
This project attempts to discover what a true "people's" art would look like. Through a professional marketing firm, a survey was conducted to determine what Americans prefer in a painting; the results were used to create the painting America's Most Wanted. This project was expanded in both scope and audience through the Internet at Dia's website, allowing visitors to see the paintings based on completed polls of over a dozen countries.
This is a link to the Most Wanted and Least Wanted paintings by country. They're actually a composite based on the answers to the survey questions.
This a link to the survey results - which analyse responses to each survey question by country.
So you ask, what is the Most Wanted Painting in the United States?
Komar and Malamid - survey results