The best GPS is already on your smart phone and it's free! Use Google maps (and WAZE if you are in an area with heavy traffic or an accident). It's more accurate than any GPS as the data is only days old instead of years old and the traffic info is real time. If you are concerned you will not get routing information while traveling, Google downloads the route ahead automatically but if you expect extended periods without cell service you can download the entire route (I just download 4 States for an upcoming trip) to your phone as an additional "safety" feature. I have never seen it necessary traveling any major road anywhere in the US thus far but there's nothing wrong with "belt and suspenders".