I have looked a couple of the routing programs, but usually just look at Google Maps to see what may be a nice path from point A to point B, looking for lines that aren't straight.....which can be difficult in SE Texas. I have used, with some success, a website called mapstogpx.com to convert the route I map on Google Maps to a .gpx file that I then load onto my Garmin Zumo XT. It works well if the route is not real complicated, but it's not always 100%. It can sometimes completely ignore one of the oddball detours I select on Google maps when looking for new roads to ride, which can be pretty frustrating. I should probably learn to use Garmin BaseCamp and cut out the middle man. I gave up on the SVTC GPS as a routing guide (unless just using it to get from A to B without any side trips) as downloading custom routes to it is just a PITA.
I used to use MapQuest as my go to map app, but at some point a few years ago it wouldn't find smaller roads that I knew existed, so I switched to Google. I looked at MapQuest a while back and it seems to be able to locate those smaller roads again, so I may go back to it. MapQuest more positively identifies FM roads vs. state and county roads than Google maps does.
When I had no GPS (or didn't feel like messing with one) I would write a short description of turns to take on a 3" x 3" piece of paper and tape that paper below the speedo on the Nomad or on the gas cap cover on the SVTC and call it my paper GPS. Took many and led a good number of rides using that as my guide. Sometimes turns would sneak up on me since I didn't usually know the exact mileage from one turn to the next. I would also often have a "going" and "return" paper GPS. Carried scissors and a roll of scotch tape to use when changing out. My riding buddies at the time got a kick out of my navigation system, but we never got too lost....
This one got me and a friend to Granbury, Texas, about a 300 mile one way trip.