Many AF-followers prefer the term 'tinplate' when talking about pure Flyer. When using AF track, a layout can be built quickly and in a smaller area than the scale counterpart. While the track is more true to the prototype than 'hi-rail,' it often requires more space and more time to build. It is strictly a personal preference issue - each has its own advantages. Tinplate offers the nostalgia of toys from the 1950's and a chance to remember the fun.
Scale provides the opportunity to create museum-quality, realistic models in realistic settings.
Hi-rail offers a combination of both. For many years, the S scale modeler needed scratchbuilding skills to have a nice railroad. Today, and for several years now, that is no longer the case as a growing number of companies provide S scale products. Narrow gauge modelers are lucky as the HO line of couplers works well for S narrow gauge. Well, that depends.