I still fly FS98 most of the time. In my cockpit, that is. Software development is another story, has to work with all versions.
I have created a few planes that really fly by the book, and I did not want to recreate them for later versions.
The big improvement of later versions is of course scenery, and the looks of your plane. Controls, panels, you can do it all with FS98 and do not need a heavy PC for all your wideview screens.
Being inside the pit, I do not care much about the looks of the plane as long as it flies OK.
Scenery - I use Europe1 among others. There is enough to get out there, and I do not fly close enough to church towers to actually enjoy their ornaments. Once I am close enough to the ground to appreciate details, I have my hands full landing the plane.