In this study, the heat transfer characteristics of the flat plate collectors with circular and elliptical serpentine tubes are theoretically analyzed and compared in terms of $\dot{m}$, $Re$, $Nu$, $h_{fi}$, $F_R$, $Q_u$, and ${\mu }_{Th}$ under various water flow rates and the standard test conditions. The results reveal that the maximum ${\mu }_{Th}$ correspondence to the elliptical serpentine design with 56% under turbulent flow, and the minimum ${\mu }_{Th}$ of 47% for the circular cross-section under laminar flow. In addition, it was found that the highest useful energy gain per unit time (493.8 W) through the system is possible when $F_R$, $h_{fi}$, $Nu$, and $\dot{m}$ are maximum and vice versa. It was concluded that, at the same area, the larger contact area in the elliptical cross-section compared to the circular would improve $F_R$ and $Q_u$ by an average of 2%. Overall, it is crucial to evaluate the thermal parameters of the thermal collector during the preliminary design stage to fabricate a highly efficient system and save time as well as initial cost.