The weakest direction in an FDM part is usually across layers
Fused deposition parts are anisotropic: strength along a layer line is typically much greater than strength across the bond between two layers, since interlayer adhesion depends on partial remelting that never fully matches the strength of continuous extruded plastic. Orienting a part so its layers run parallel to the expected load, rather than across it, is one of the single highest-leverage decisions you can make for a functional part, but it is not free: the orientation that best aligns layers with load is not always the one with the least support material.
How the comparison works
Each option you describe is scored on whether its layers align with the load direction and how much support material it needs, with the alignment penalty weighted more heavily for tension and bending loads (where interlayer weakness matters most) and less heavily for compression (which loads the whole cross-section more evenly). The option with the lower combined score is presented as the best fit, with the tradeoff between strength alignment and support burden made explicit rather than hidden behind one score.
Worked example
A tension-loaded bracket, standing upright (layers aligned with load, support burden 1) versus lying flat (layers not aligned, support burden 0): standing upright wins under a tension load, since alignment is weighted heavily here, even though it costs more support material than lying flat.
A common mistake
A frequent error is optimizing strength-axis alignment for one obvious load direction while ignoring a secondary load the part will also see. A bracket mainly loaded in tension may also see an occasional side impact; if that secondary load matters, weigh it in the comparison too, rather than treating the primary load as the only one that counts.
Limitations
This compares layer-direction alignment and support burden qualitatively; it does not calculate a safe load, factor of safety, or actual measured layer-adhesion strength for your printer and material. Validate a load-bearing design with a real test part before relying on it.