For me its all of my Atlas O PRR, Conrail, and Amtrak diesel Locos- all those made during the Jim Weaver era. They look too good- even if the electronics are a bit dated, they are hear to stay!
Also My 3rd Rail Brass Steam Locomotives of the PRR. They too look too good to let go even if the electronics and smoke are dated.
My Demonstrator locomotives. Since many of them are "Display Queens" no reason to worry about the electronics!