<p>The performance of parts produced using fused filament fabrication, a widely adopted additive manufacturing technology, is significantly influenced by build orientation. While previous studies have explored the effects of part orientation on mechanical and geometrical properties individually, their simultaneous interactions remain underexplored. This study addresses this gap by investigating the combined impact of build orientation, defined by three angles (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\alpha ,\beta ,\gamma\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>α</mi> <mo>,</mo> <mi>β</mi> <mo>,</mo> <mi>γ</mi> </mrow> </math></EquationSource> </InlineEquation>), on tensile strength, flatness deviation, and surface roughness of PET-G (Polyethylene Terephthalate Glycol) specimens. The methodology consists of two stages: (i) an experimental campaign to establish the relationships between orientation angles and the output variables, and (ii) a surrogate-based optimization approach, employing the weighted-sum method and genetic algorithm to identify configurations that achieve optimal compromises between mechanical and geometrical properties. Results demonstrate a strong dependency of all outputs on the orientation angles, particularly the out-of-plane rotation, and a negative correlation between tensile strength and geometrical quality metrics. Optimal performance is confined to specific regions of the input space, emphasizing the importance of a precise orientation control. A graphical approach, inspired by Voronoi-like regions, illustrates the interdependencies among outputs and maps achievable compromises in the output space. These optimal zones correspond to limited regions in the input space. Moving away from these configurations results in a rapid decline in performance, underscoring the sensitivity of the process to build orientation and the need for tightly defined parameters to ensure high-quality parts.</p> Graphical Abstract <p></p>