I am a user of vatsim, and thus is more used to the 4-lettered ICAO code.
Also, the ICAO code for airports tells more about it's continent/location.
for eg,
american airports are prefixed as K***
South east asian airport are prefixed as W***
Australian airports are Y***
Isn't this easier for searching, classifiying etc?
Highly suggest ICAO use.
(should there be any reason for IATA use, please enlighten me)