There is no 'best app' for planning a trip or deciding which places to see just like there is no best helmet or best bike or best tire or best oil :-) .. sorry I am not trying to be a smartass, I really am not. Find an app that you like to use and it will turn into the best app for you!
1. Several Apps Try out a few apps and see what works best for you .. InRoute, MyRouteApp, Calimoto, Relive, Scenic, Rever, HDPlanner, Mappite, etc are some of the popular ones. Most of these have option of navigating directly on the cell via app or then downloading gpx and uploading it to the Nav system. Most of them can track a ride as well
2. Google Maps
Google maps is also good to create route on desktop and send directions to phone. You can add upto 10 waypoints but can always drag and drop the path if you need more then 10 waypoints. If you dont prefer highways then uncheck highway/toll under Route Options and google maps does a pretty decent job. Its still not the same as backroads because Google Maps will route you through cities etc when there is an option. Google maps can track as well based off location but not as specific as the others.
3. Google My Maps
Google My Maps (not the same as Google Maps) can be used to create route but wont export as GPX. You will need to use a third party tool to convert kml/kmz to GPX before you can throw it on your nav. No native cell navigation option
4. Garmin BaseCamp
Garmin Basecamp is an application to install on your desktop to create routes/GPX. It is good but needs a little more effort and requires a separate GPS unit/app to create route on desktop. No native cell navigation option
5. GPX Files Import
GPX files cant be imported to google maps or apple maps but you can always use the above mentioned apps on the cell phone to open a GPX file for navigation
6. Satellite Based Trackers
GPS trackers like Garmin and Spotwalla are great for tracking rides but they do come at a cost plus monthly subscriptions. If you are looking purely at tracking rides, these have no competition. They are one hundred percent dependable whether your cell phone has service or not. You can also use these to share your location and track/ride with family and friends.
7. Location Sharing
Google Maps location sharing can also be used if you want to keep your family/friends updated on your location. It is cell phone service dependent. Which means if you are on Dalton Highway in Alaska, your family probably has no clue where you are other than your last known location. Life 360 is another popular one but I am sure there are more. My vote still goes to Satellite based units (though they come at a cost)
Use the below to identify good backroads and interesting places etc and then use one of the above mapping applications to plot out a ride .. safe travels!