I like the Garmin RV600 series and RV700 series.
Features I like the most:
1. Voice command for hands free control of functions
2. Elevation feature that allows you to view how steep hills are
3. Garmin Link to Smart Phone for weather alerts, live traffic, photoLive cameras, and Foursquare recommendations for restaurants, gas, banks, etc.
4. Ability to make and receive hands free phone calls.
5. Can input your RV's size and it will route you around things like tunnels.
A number of new GPS units have similar features. I think there are two or three brands at the top that would be adequate. Just what features you like best and how the user interface works for you. You can try some out at camping world.
From my research before I purchased my RV660 Garmin, truckers rated Garmin and Rand McNally as the best. Garmin seemed to be more reliable.