I want things scale, but unless you put a cap on the amount of scale (detail) you'll never be pleased. If you want scale and want to model a specific RR, chances are you're going to have to compromise. I've found I can usually find a scale piece that is exact for the RR I want, but finding scale engines that are accurate of the RR is hard to do.
The "Close Enough" concept works for me. Most scale pieces of rolling stock are bigger than the traditional pieces, but they come at a higher price and finer/more fragile detail. If you have kids, things will get broken.
Of course, you can buy traditional pieces and upgrade them if you have the time and patience.
Buy what you like, learn to become a "plastic surgeon" and modify it if you want/need.
