This is timely, as I am evaluating CalTopo for use in laying out courses. ( caltopo.com ). I think it suffers from the same problem that the onthegomap.com site was first thought to have, i.e., a resolution of only 10 meters. I have contacted them to see if they can do better.
As I was writing this I found an option in the Config menu to change units to "feet only." (I would like to see meters as an option there as well.) The question I have is whether looking at "feet only" is simply a false displayed resolution, or a "real" resolution.
I compared measurements on a short segment of road (with some hills and curves) between Caltopo and MapPedometer. Caltopo reported 5571 feet, and MapPedometer reported 1.6979 km (rounds to 5570.5 feet). Pretty close.
One thing I do like about Caltopo is that with the other options, I am clicking the next point blindly, which means eyeballing the tangents and SPR through curves. With Caltopo, a line stretches from my last clicked point to the cursor position, which allows me to see where the line will fall when I click the subsequent point. I also appreciate the ability to split routes, extend routes, and place options on the same map. The link below shows examples of this.
Having said all this, mapping out road courses is not what Caltopo was really designed to do. It really shines in the backcountry, for laying out wilderness routes on and off trail. See, for example, a trip I did in September 2017: Wind Rivers . It does some really cool stuff with elevation, terrain, and slope statistics.
I currently use Map Pedometer or GE, though my preference tilts to Map Pedometer.