This paper addresses the critical issue of selecting the optimal mechanical test method for the efficient development of process parameters in Automated Fiber Placement (AFP) technology for manufacturing thermoplastic composite structures reinforced with unidirectional (UD) carbon fibers. Four commonly applied test methods were analyzed: Short Beam Strength (ASTM D2344), In-Plane Shear (ASTM D3518), Compression 0° and Compression 0°-90° (ASTM D6641). Each method was evaluated based on four key criteria: sensitivity to AFP process parameter changes, repeatability of results, ease of specimen fabrication, and clarity of result interpretation. Test panels were manufactured from Carbon Fiber Reinforced PEEK Composite (CF/PEEK). Three distinctly varied AFP process parameter sets were employed for specimen preparation, intentionally designed to induce clear differences in laminate mechanical quality. Based on the conducted analyses, the Compression 0°–90° method was identified as optimal, demonstrating high sensitivity to AFP process parameter variations, low result variability, reliable fabrication of flat panels, and straightforward interpretation of test outcomes. Additionally, the conducted studies highlighted significant challenges associated with directly applying existing ASTM standards, originally developed for thermoset composites, to thermoplastic composites manufactured using AFP technology. Issues such as panel deformation, complex result interpretation, and atypical failure mechanisms arising from the significantly higher ductility of thermoplastic composites. These challenges emphasize the necessity for developing dedicated testing standards specifically tailored to thermoplastic composites produced by AFP technology. Selecting and indicating a specific test method enables faster and more efficient development of AFP process parameters for a wide range of thermoplastics reinforced with various fiber types. Consequently, this will significantly accelerate the process of introducing new composite materials into industrial production, supporting further advancement of automated manufacturing technologies for composite structures in aerospace and other sectors.