In America, it has to be LAX (Los Angeles). It's also my home airport so I might be a little biased. But where else can you see people from ALL over the world in one airport? Asians, Latins, Europeans, and of course all the weirdos from here in the states. PLUS, more often than not, you're standing in line with someone famous or from a reality t.v. show and you might not realize it right away.
As for other airports wordwide, Madrid, Spain has the most beautiful female employees I have ever seen at any airport. This includes everyone from ticket agents, to fast food workers, to flight attendants (ESPECIALLY flight attentdants!). Tokyo has the friendliest people by far. Frankfurt, Germany isn't bad either.