The benefits of the fused filament fabrication (FFF) method, including its simplicity, affordability, and accessibility, have made it the most commonly used additive manufacturing technique. Polylactic acid (PLA) is the most widely used material in FFF, but its use has been limited by low mechanical properties and a small processing window. To address this, PLA composites are used to improve its properties. Correlating mechanical properties with process parameters is crucial for producing high-quality composite parts. This study investigated the effects of material and process parameters on mechanical properties, such as tensile strength and elongation-at-break, using a customized Delta Rostock FFF printer. Two types of filaments were used, pure PLA and PLA/Aluminum composites. Printing speed (10, 20, and 30 mm/s) and raster angle (0/90, −45/45, and −30/60) were selected as process input parameters. The Taguchi method was used for the experiment design, and signal-to-noise ratio analysis was used for statistical optimization. The optimal values for achieving maximum tensile strength of 61.85 MPa and maximum elongation-at-break of 17.7% were determined. Furthermore, the signal-to-noise ratio analysis indicated that the filament type had the greatest influence on the tensile strength, whereas printing speed had the greatest impact on the elongation-at-break.