I suppose LAX or JFK might be the most common in the U.S. also ATL might be one
I doubt folks refer to ORD as "yeah, I arrive at "ORD" around 4pm" Most folks would say "O'Hare" right? same goes for LaGuardia and Logan maybe.
I guess which airports are BAD ASS enough that everyone knows their code v/ just being referred to by the city they are in??
I guess it has a lot (if not everything) to do with how well the code reflects the airport name and/or city...