You likely already have the best GPS built right into your smart phone. Now that Google Maps has purchased WAZE, the real time traffic is the best I have ever seen and the routing is every bit as good as any stand-alone Garmin I have ever owned. I use one of the most recent Garmin releases in when traveling in the RV but I then turn on my Google Maps when I am getting close to the destination as I know that Google will do a better job of getting me through those last few miles.
If you are needing more than just routing information like campgrounds and food stops, this information is all going to be out-of-date even on the most current GPS with the most current software update. The GPS database simply cannot store enough to compare with what can be handled using the internet for your searches. For campgrounds I like RvParky.com (there's an app as well) and you can use RvParkReviews.com to see what others think about that choice. I also use Google Earth (A LOT!) to see what the park actually looks like both from above and from a street view. You would be surprised at what the campground says about itself and then what the camera shows.
Save your money on the GPS purchase (as always, my opinion). If you like a larger display then a small android based tablet will give you the same thing with a larger screen.
What I post is my 2 cents and nothing more. Please don't read anything into my post that's not there. If you disagree, that's OK.
Can't we all just get along?