Routes provide the hardware. Sessions provide the "software". It is the sessions that decide where you go and what you do.
Some creators only build routes and provide you with only the layouts and scenery. Some also build sessions with directed objectives ("drive here, load/unload that" etc).
A growing number of sessions are appearing that are variously described as "Free Roam" or "Quick Drive" where all the consists are in place and the industries fully configured but you decide where to drive and what to do.
But as pointed out above, your preferences will decide what is the "best" layout with the best "action".
Me, I prefer Australian narrow gauge steam era routes and action of
calculadora de finiquito. Driving a long double stacked container freight with triple diesels is, to me at least, boring.