It's pretty awesome to make maps of the real deal, and people can relate to that. Not every place takes to being put into a game (as games have limitations), but many places fit rather well. Like Sprawl-Mart Just one more thing added to Roane County Tennessee.
I am torn on this... I like to make original maps because I can be more artistic and imaginative with my work, however I also like real maps, and the attention to detail with them. Same as above, I will pretty much explore any decent map for BeamNG, real or fictional.
You can make a real neighborhood into this game, you just can't translate the details quite as finely and 100% all the time, not without the FPS going on vacation on you, or the game just plain not being able to handle 'that many items'. Screenshots from an in-dev version of Roane County, Tennessee, Screenshot is "A neighborhood in Kingston, TN".
Even in fictional maps, if for say you have way to many trees, it starts to really mess with framerate stability.
Both. Making a real place in details is awesome, even if some modifications are generally required to get a decent FPS. Making a fictional map is as interesting, because the creator has the choice to make something completely different. Those maps can be really great if enough work is put into them (by that, I mean that a fictional place that looks too bland or generic might not always be that interesting).