The best orientation for a joint depends on what kind of joint it is
A flat mating face wants to be printed directly on the bed, since the bed produces the flattest, most dimensionally consistent surface a printer can make. A round hole or shaft wants the opposite: its axis should run vertically, since a horizontal round feature is built from stacked layers that approximate a circle less smoothly than one built with the axis perpendicular to the layers. A threaded boss wants its axis vertical too, so no horizontal layer seam crosses partway up the threads, a common cause of a rough or binding printed thread.
How the comparison works
You select the interface type and describe two candidate orientations by whether the interface sits on the bed in each. The tool matches your interface type against the orientation that generally suits it, favoring bed contact only for a flat mating face and favoring the opposite for a round or threaded interface, then names the better-matching option while noting your stated support tolerance for that specific interface.
Worked example
A threaded boss, low support tolerance for this interface, Option A has the interface on the bed, Option B does not: since a threaded boss wants its axis vertical (interface not on the bed), Option B is recommended, with a note that low support tolerance here reinforces choosing an orientation that avoids support contact at this specific feature.
A common mistake
It is easy to pick an orientation purely for overall part strength or support burden and forget that one specific interface needs its own orientation logic. A part can be correctly oriented for its overall strength and still have a threaded boss with a seam crossing the threads, simply because nobody checked that one feature separately. Treat each critical mating interface as its own mini-decision.
Limitations
This compares print orientations for interface flatness, circularity, and support contact qualitatively; it does not measure actual dimensional accuracy for your printer. Confirm the interface on a test print before committing an assembly with a tight fit requirement.