I've used a Garmin for years and find it's the best/easiest to use.
Don't know if an RV specific one would be all that much more useful. Got my last one with a 5" screen at Costco for $145.
My new truck has the built in Nav and Onstar. I like the nice Onstar lady - she's quick at finding stuff and downloading it into your Nav. She's not around though, to tell you to get in a specific lane for a turn-off ahead. But she will tell you to have a nice day