I totally agree, Tony. Its all down to personal experience and preference.
For example, I have no idea what most of the commercial routes are like. As my interest is building, then I'm unfortunately not able to justify the outlay, and have no idea what I'm missing. Consequently, my "best 3" routes will be totally different to anybody else's.
Apart from that, threads like this can be really unfair towards those route builders who have produced freeware routes that don't fall into the category that a number of MSTS "players" like driving. For example, I believe that the GWR Toddington route is one of the best routes as far as realistic "across the fields" scenery is concerned. But it is a short route, its not a mainline route....so will have limited appeal to many who will read and take part in this "poll"; they want to drive modern mainline!
Another route I believe falls in to the same category ast Toddington is the Canadian route London & Port Stanley.....these are two routes that I like...and have the quality I aspire to in my own work. And I might mention that the one route I have produced has not been mentioned in this thread.

I wonder why.....