I have and love a RND RV GPS. Mostly because of how the POI are organized and ease of use.
I had a Magellan and could not stand the interface - yet my best RV friend/ co-traveler has one and loves it.
I had and still use a Garmin Nuvi from my wife's car. Traffic information beats the RND by far.
POI can be added to all GPS units. I do like the ability of Garmin units to take files from MS Streets and Trips directly.
I never use the GPS to plan the route. I plan my daily route on the computer, then add the waypoints I need to follow to the GPS.
So I often drive with both the RND and the Garmin on the dash. The DW watches the Garmin for potential traffic issues when we are near large cities, and helps plan a route around them.
WARNING - any GPS is only as good as the source data. If roads, bridges, underpasses have been updated since the source data date - you can get wrong directions.
WARNING # 2 - Never, ever, use a GPS set to "Shortest Route" with an RV. It will send you down roads never designed for a vehicle of that size.
WARNING # 3 - If you are going through a complicated city you are not familiar with - like Nashville, TN - do some research before starting out. Know which highways you intend to take. Look at the exits/ interchanges on Google Earth/ Bing Maps and know which lanes you need to be in two miles before an exit/ change of road.
A GPS is ADVISORY - never expect it to be perfect.