Obviously ETK Seats for the Covet! I have yet to find anything that surpasses it in both quality and pure ingeniousness.
I like a whole bunch of mods. Some good ones are the Dansworth bus, the oldsfullsize, the the me262, the etk s series, the Miramar z, and a whole lot more. A lot. Like seriously. A lot. I also recommend the busfag.
Sounds in Olds fullsize are killing fun for me. Anyways there is no best, because best depends so much from your definition of best and we probably never will agree on definition of best, everyone looks different things in mods.
Config packs. This is why I have a hundred-some of mods. I also like any/all working/crashable plane mods.