I believe the more tool at hand, the better. I have the Garmin RV660. It's pretty good. Using it in areas I already know, I do know better, shorter ways to get to the same place.
Our Ram truck's gps is worse. Google map on the phone when there is coverage is the best. I don't depend on any one of them. Just use them and look at the road signs.
Using a paper map for longer trips is easier to see the big picture. Then use the GPS or Google to fine-tune the trip.
The old Garmin map programs were great. Plot the trip in the program and then plug it into the gps. I would break the trip down by leg or day and use the GPS that way. Basecamp suck compared to the old mapsource program.