Here in Ohio, bike club routes are often very good starting points. The routes have been refined over many years. It still amazes me how a boring farmland area can have all these side roads that are quiet and scenic. Woods and creek valleys, and essentially no cars.
I posted about planning with heat maps in
this post.
Not every "popular" road is actually nice to ride, some may be just the usual way to get out of town, or connect between some better roads. And some riders just don't have a clue and pick really annoying or dangerous roads.
Yes, like brentlarue posted:
Strava is great, but I think their heatmap can be misleading due to the way they let user's interact with it. It seems commuter, road biking, touring, MTBing, and road racing are all mixed into a single heatmap. That has led me sometimes to busy main roads which commuters enjoy, but I do not on a road bike. Or I've been sent on single track and gravel when on a road bike with skinny wheels far from home.