@A. Wells @John H Forgot about the earlier post. I've shared these photos before showing the difference between the Lionel "S sized" semi-scale, Lionel "O" scale, MTH Premier and K-Line cars. To me only the Lionel scale and K-Line scale cars look good together. MTH would be OK if that is the only type you run, but they are tall. I have the Lionel 6-17589 and 6-27521 stack cars. Very detailed including the doors which open after moving the locking bars.
If I recall correctly the center car is MTH Premier, left is Rail King and right is the Lionel semi-scale.
Lionel semi / RailKing / MTH Premier
Here the lead car is the Lionel scale and the K-Line following. There is a difference in the containers. K-Line tend to be square (perhaps the older style containers) whereas Lionel is rectangular (taller) (perhaps the more modern style container).
I have a video posted of the Lionel and K-Line containers running on an earlier post 3/31/2021 on the forum https://ogrforum.ogaugerr.com/...2#154730473387022022