I'm a Garmin fan myself, but my RV came with a TomTom in-dash. I never could get used to it - the interface was just different enough to make me pine for a Garmin, the navigation style is a bit different in routing, destination selection, etc. I finally removed it and replaced it with a Garmin.
I have a lot of RV related Point-of-Interest (POI) files that I install on my GPS systems. I found that easy to do with Garmin and virtually impossible with TomTom. It could be I just didn't dedicate as much time to finding a TomTom solution. However there are a lot of POI files available for both TomTom and Garmin and many are RV related. If you're comfortable with using them you should be fine with either system.
One thing I liked about TomTom that Garmin doesn't have is incremental updates. TomTom users can submit minor map changes that can be downloaded and installed on your GPS. With Garmin you have to wait until Garmin updates the maps, usually quarterly.
I found the maps in the TomTom to be less precise than those in Garmin. In one case I discovered a National Park that it couldn't find or navigate to, but once I was there it knew how to navigate home. I contacted TomTom about this and their response was it must be a new National Park, the park may be "off-road", and/or the roads were just recently built going to the park. The park has been around since the 40's along with the main hiway to it and the park HQ is right on the hiway. In fact the hiway has been rebuilt about 3 times in the past 40 years and it's a major trucking route, and it knew where the hiway was when I was there, just didn't know how to get there.
I'm not saying TomTom is bad, just different. If you're used to using a TomTom you may not be happy switching to Garmin. And if you're a Garmin user like me you may find problems switching to TomTom like I did.