Over the last 30 years, I have accumulated quite a few engines and rolling stock from LGB, Bachman, USA trains, Lionel Large Scale, Aristocraft, and hand built. I have too much rolling stock to afford the time or money to change. I have found that the LGB and the larger Kadee couplers work well with all the other knuckle couplers so I will put a car with Kadee or LGB couplers as a transition car. I also have a few transition cars with one manufactures couplers on one end and another on the other end.
My 13 by 26 double track layout is about fifteen years old now and since starting, I have used almost 3000 pounds of small rock ballast. I do not know where it goes but I need to add ballast every year. No matter how hard I try to keep the track level, I still wind up with dips large enough to cause smaller Kadee and sometimes larger knuckle couplers to slide out allowing cars to separate. I have gone back to hook and loop couplers on a lot of cars because this never happens with these.
Happy railroading,
Don