3D printing has transformed manufacturing by enabling the rapid production of functional parts without the need for jigs, fixtures, or moulds. To fully exploit its potential in precision manufacturing, it is essential to evaluate the dimensional accuracy of different printing architectures. The present study compares the performance of Cartesian and Delta FDM printers in terms of dimensional accuracy, shape fidelity, and alignment precision. A novel geometric benchmark artefact was developed to evaluate GD&T parameters and assess within-build repeatability across multiple features. Both printers were operated under identical process parameters and material conditions. Dimensional deviations between the printed parts and the CAD model were quantified using an optical 3D scanning technique. The results show that Cartesian printers achieve higher accuracy in planar and fine-detailed features, whereas Delta printers perform better for curved geometries. The Cartesian printer exhibited a mean negative deviation of −0.36 mm, while the Delta printer showed a mean positive deviation of +0.23 mm. Although the Delta printer demonstrated slightly lower overall error, it exhibited greater flatness deviations. These findings establish a systematic framework for precision evaluation in FDM and highlight the complementary strengths of Cartesian and Delta systems, providing guidance for printer selection based on application-specific requirements.