We've been researching the same topic lately. We want an RV that we can live out of for a year, but are avid rock climbers and need something that is off road capable enough for us to get to climbing areas. No crazy 4x4 trails, but something that can handle moderate rutting and washboarding as well as tight turns. Given that we'd be living in it full time, we'd want a bathroom and something big enough that I can stand in and fit in the bed (I'm 6'4"). We don't intend to move camp more than once or twice per month, so something where we can detach the RV from the vehicle is a major plus.
For trailers, we had been looking at things like the RPod, the Geo Pro, and the Little Guy Max. All of these claim to have off-road packages, but in practice, none of them seem very capable. Also, none of them are even close to being four season. Now, we're looking at options like the Lance 1475 and ORV 18RBS, both of which look like good four season options. I'm not sure how off-road capable either of these are though.
Another thing that we've been considering getting a bigger slide in truck camper. Some of the bigger models with slide outs seem pretty spacious. The good ones are pricy and you need a lot of truck to haul them, but they can definitely go places. You end up with a pretty tall vehicle though, so I do wonder about clearance. Also, some of the nicer models can be used off of the truck, so that meets our leave-the-RV-behind requirement.
Finally, we considered a class B setup. The Sprinter van conversions are really popular with climbers these days. I don't think they're right for us though. They are super expensive (easily $150k), fairly cramped, and you have to break down camp every morning when you want to drive somewhere.