<p>Selecting the most suitable high-performance polymer for a printed circuit board (PCB) substrate with low coefficient of thermal expansion (CTE), superior thermal stability, dielectric properties, and cost-effectiveness is challenging. In the present work, a hybrid multi-criteria decision-making technique was used to select optimal PCB substrate materials for modern electronic systems. Polyether ketone (PEK) reinforced with fly ash particles (PEK/FA) composites were prepared and evaluated for their physical, electrical, thermal, and mechanical properties. In addition to prepared PEK-FA composites, other high-performance polymer composites reported in the literature and conventional material (FR 4) were evaluated using the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method to rank the alternative materials. Seven decision-making criteria, such as coefficient of thermal expansion, thermal conductivity, dielectric constant, dissipation factors, thermal degradation temperature, density, hardness, and cost, were considered for the study. The relative weights of criteria were calculated using the Criteria Importance Through Inter-Criteria Correlation (CRITIC) method. The results indicated that cost (23%) and electrical properties (18%) are the most influential criteria, followed by thermal properties and density. The TOPSIS method suggests that the PEK/FA composite reinforced with 30 wt.% FA is the most suitable material, with a performance score of 0.811, while the PEEK/AlN composite is the least suitable, with a performance score of 0.401, for modern PCB applications. The sensitivity analysis was conducted to assess the consistency of the ranking order. It is observed that the ranking order of materials is quite similar, especially among the top three in each case.</p>