Which track gauge and standards should I choose?
12mm gauge is widely used, and there are many fine layouts which use it. It is the one gauge for which commercial track is readily available, from both Peco (HOm) and Tillig (TT) , although the range is limited, and indeed many modellers use hand-built 12mm track. The main question is whether you would be satisfied with the underscale appearance of 12mm or whether you would prefer a gauge closer to the prototype. A secondary question is if you adopt 12mm gauge, do you use Intermediate or Fine standards? If you build your own track you can use either, although most people use Intermediate. One disadvantage of 12mm gauge is that the wheels are closer together, which can limit the choice of gearboxes and motors in locomotives.
[pictures of track]
14.2mm is most likely to appeal to those who want to build fine scale track to prototypically correct gauge, and relish what challenges there are in doing so. The standards themselves are pragmatic; the Fine standards are not S3, they are effectively a scaled down EM pushed out to correct gauge, and are fairly easy to employ. The wide range of good-looking wheels available is an added bonus. Also, etched locomotive kits reduced from larger scales can usually be built without further work to this gauge, not always true of narrower gauges. The main challenges are with locomotives with outside cylinders, and sometimes valve gear, where the slightly thicker-than-scale wheels can lead to tight clearances; for example, one dodge is to push the cylinders out slightly.
13.5mm gauge is most likely to appeal to those who want something closer to the prototype, whilst avoiding the fine clearances in 14.2mm. To get the most advantage though, you need to use Fine rather than Intermediate wheels, with the track standards to suit.
In the remainder of this guide you may find further things to help you with your choice; a more detailed look at the track issues in particular is recommended. One thing which could be worthwhile would be to try a wagon kit with both 12mm and 14.2mm wheels (easily swapped if you position the brake gear carefully), and see what you think of the difference. A recommended choice would be one of the Society's Parkside wagon kits, with the Society's own Intermediate and Fine wheels.
[need end on picture of 12mm vs 14.2mm wagon]