as you have probably noticed, some airports(JFK)(Heathrow) are far more deatailed than others. I would not go as far as to say they were completely 'realistic' but they do alow the viewer to easily depict what airport it is.
The airports that i am farmiliar with in real life like YBBN (brisbane, australia) have buildings in the same place on FS, but they are not the same buildings, but they are close enough to tell that the airport is infact YBBN.
As far as aircraft go, it is quite hard to tell which is the most realistic. I take it you are referring to the default aircraft. Also, do you mean realistic in look or in the way they fly?
Starflyer, i am in no way trying to contradict you or change your questions, but i am just trying to get the specifics in order to help you.
If your could reply to this post then i will be able to help you further.