21 inch, ie 80 ft scale plus vestibules), are prototypical for nearly all RRs. there were some shorter real cars, but they were not that common that I can find. So if you are interested in models of real train cars, 21 inch is probably the way to go.
One way to avoid the sharp look is to build an around the walls layout rather than an island. The overhand on curves is not nearly so noticable from standing inside the curve than outside.
