I have used 6 volt systems for the last three trailers (10 years) and have been very happy. I think it is a matter of preference, if you can get an equivalent number of amp hours. that is the true measure of how much power you have to run things.
Adding solar is a sound idea. We have a cheap set of two panels, that make around 19 volts, running though a controller, that keeps it at 14 volts, and keeps the batteries well charged. They aren't mounted, so I just put them on top of the rig when I park and put them back in the box when we leave. I rarely run the generator, and we boondock for up to a month at a time (archery elk season in Oregon). The genny only runs if there is a real cold front for several days, or if we need to run the water heater or A/C.