@enriquerrr I have never had or used either type, nor any sort of camping trailer.
However, strictly in terms of physics and logic, a 5x8 will be lighter and smaller, making it easier to pull with a lightweight vehicle, at the expense of interior space for onboard equipment and occupants.
If both options are well within your vehicle's towing capacity and you aren't going to take it into tight places (such as out on the trail), all else being equal, you wouldn't be hurt by getting the 6x8, for the extra space. Navigational convenience would be expended in favor of potentially better outfitting, more space, and more comfort.
This could also quickly become an apples-to-oranges comparison if you consider vastly different types of trailers in the same size range. Some 5x8's could be better equipped than other 6x8's, for example, depending upon production year.
I would generally recommend the larger one for all purposes UNLESS you are specifically looking for that navigation advantage.
