Ridiculous question, right? Why would an adult ask someone else what size clothing to buy for themselves? It's a matter of personal preference and what fits, isn't it?
And yet, similar questions are asked and answered again and again on model railroading forums. For example: "What scale should I choose?"; or "What railroad should I model?" Some of this is the inevitable impact of new people joining the hobby – as many do at this time of year (and that's a good thing).
Back to our shirt analogy, I think it's important that these newcomers get the best advice we can give. After all, a bad fit, whether in the collar or on the layout, is uncomfortable. But because it's really about personal preference, I wish folks would be more inclined to give advice that encourages the questioner to explore his or her own preferences by seeking out layouts to visit and trying equipment on for size in a hobby shop or at a train show. That would be better than the N supporters touting 1:160 and the HO fanatics proclaiming the superiority of all things 1:87.1.
There are benefits and limitations to every scale and gauge combination. So helping folks explore the alternatives to let them choose their trade-offs would be a real benefit. Having said that, I have no patience with the whiners who lament, "Well I really like O scale, but it's so expensive … and HO won't fit in my space … and N is too fiddly … and maybe S but there is so little available". That's often just a bored cry for forum attention and unfortunately does not often enough receive the stony silence it deserves.
When people are truly looking for guidance (and not just for eyeballs), I hope we can all think of helpful things to suggest that would give newcomers ways to experience the pluses and minuses of the scale(s) they are considering with a minimal investment of time and money. Handling equipment at a train show or hobby shop, building an inexpensive kit or two, visiting club layouts, etc., etc., would give these folks a better idea of their own preferences and interests. That should help them find the best "fit" for their long term comfort and enjoyment.