The purpose of this study was to compare the performance of polylactide (PLA)-based materials shaped by the traditional injection molding technique versus three-dimensional (3D)-printing additive manufacturing. Comparisons were performed not only for neat PLA but also for its thermoplastic polyurethane elastomer (TPU) blend and for its E-glass fiber (GF)-reinforced composites. Performance comparison of the injection-molded and 3D-printed specimens was especially conducted to compare their mechanical properties (strength-modulus-toughness) by tensile, flexural, and fracture toughness tests. Other comparisons such as their macro-level appearances, fracture surface morphology, and thermal behavior were also performed by photographic images, scanning electron microscopy, differential scanning calorimetry, and thermogravimetric analysis. It can be concluded that the use of 3D-printing in the shaping of neat PLA and PLA/TPU blend was generally very beneficial; on the other hand, due to the differences in the orientation of the GF reinforcements, there could be certain reductions in the mechanical performance of PLA/GF and PLA/TPU/GF composite specimens.