Basement ACs are usually heat pumps, meaning they can provide heat as well. As in all heat pumps, with decreasing temps, the amount of heat that can be extracted diminishes and most just shut down the heatpump and go to gas when the temps approach freezing. Use of a basement A/C unit may give an RV an overall "lower" profile in terms of total height, but unless you are in remote areas, height is generally not a problem. Servicing a basement type unit has to be more complicated/expensive than a rooftop unit. There are a couple of variations on rooftop units. You will find RVs with multiple rooftop units that are not ducted such that the cold air blows out only beneath the unit and this is kinda bad from a cold air distribution standpoint. Then, there are "ducted" roof ACs which have multiple output ducts in the ceiling throughout the RV just like a basement AC unit. FYI, Winnebago, after years and years of installing basement ACs in their motorhomes have just, this year, gone back to rooftop units. Not sure of the reason...just a fact for your data gathering.
Lots of folks complain about the basement AC being "marginal" at best for keeping the RV cool in hot weather. Can't speak for the rooftop units but they may do better.
Not sure if one or the other is "best" from a reliability standpoint. All I see is that you do get some "heat" from the basement units in 40-50 degree temps whereas you're on propane for heat with a rooftop unit. If you're in a campground and plugged into shore power, you're heating on someone else's dime, if you're on propane, you're spending your money.