If you take a close look at the picture of the freight yard above, the two PRR hoppers in the foreground have link couplers. They couple every time, even on speed step one. Ignoring the link coupler alternative, I find that many of the knuckle couplers will not latch at typical yard speeds. The most reliable are the SHS/MTH couplers. Even some of the electrocouplers on the engines do not fasten with a light bump. When I see the train pulling forward and not coupled I just reach over and push them together by hand. Supposedly a small bit of powdered graphite will improve coupler performance but I have not done that.
My AM Budd cars couple pretty well, but I only uncouple the engine from the passenger sets so the entire mass of the 6 car passenger set helps a lot.
When I find cars with good working couplers I try to place them where I will be coupling and uncoupling. Short of that I just live with it.
