I don't think Federer, Safin or Moya are more popular in the U.S than Andy. His unpopularity seems only obvious among those people who watch or play lots of tennis. Generally I would say he is relatively popular in US or elsewhere.
For me, it's Federer. Nobody plays tennis like he does, no idea how he is like off court but I like how he carries himself on court. Most importanly still the tennis he plays, freaking awesome.