We've used our Garmin RV 760 for several years now, and it's done well for us. If/when it ***** out, I'd likely look to the RV 770 as a replacement. Just be sure you get the RV specific unit and not the trucker's version as the truck version will try to route you on truck routes only in metro areas. We had one for awhile several years back, and it would sometimes send us on some fairly circuitous routes. As for the RV 760/770, we particularly like the low clearance protections, the size of the screen, and the lane guidance, both verbal and on the screen. With the unit mounted on the dash within easy eye sight, this last is of particular value, especially on travel days like yesterday when we had to navigate through Dallas/Ft. Worth.
To be fair though, keep your expectations realistic when it comes to any GPS unit. None are perfect, and all will occasionally send you on a less than best route. You need to use common sense. There have been times when we've used google maps or other smart phone based apps as a back up or sanity check to a route that the Garmin is sending us. In the vast majority of cases, the Garmin was spot on. But, there are always those exceptions.