As you may know my town of Calamity features a railroad with the current configuration having the tracks running parallel to the edge of the board and then cutting diagonally across the center board while crossing the stream and then off the long edge of the board.

One of the things I have been struggling with is scale. I have enough equipment for an S Scale passenger train which is good but if I want a freight train then I'll have to scratchbuild all the rolling stock. If I go with O Scale narrow gauge I have a lot more equipment available including locomotive choices that I don't have in S Scale. Straight O Scale is just to big, but by going with narrow gauge O scale, in this case On30, the proportions are just about right.
This is the American Flyer S Scale Passenger Car. The door is just about perfect for the Wargames Foundry cowboy. Its going to be a little short for Black Scorpion miniatures

This is the Bachmann Spectrum On30 Passenger Car with our same Wargames Foundry cowboy. The door is definitely on the tall side, although a Black Scorpion miniature might look right at home.

I'm leaning towards the On30 stuff, a direction that a number of other forum members have already jumped into. My preference would still be S Scale but that lack of equipment and just general availability is a huge issue. For a more rambling discussion on the subject hop over to my blog:
http://wargamesandrailroads.blogspot.com/2013/04/s-scale-vs-on30-for-calamity.html