In this article, we make a comparative geometric and numeric analysis of the optimal strokes at low Reynolds number using two specific rigid links swimmers: the Copepod swimmer, a symmetric swimmer introduced recently 28 and the historical three-link Pur-cell swimmer 25 where the cost to minimize is the mechanical power dissipated by the fluid's viscous drag forces. This leads to a sub-Riemannian problem which can be analyzed in this rich framework. In particular nilpotent approximation can be used to compute strokes with small amplitudes and they can be continued to compute numerically more general strokes. The concept of geometric efficiency corresponding to the ratio between the displacement and the length of the stroke is introduced to analyze the global optimality. The role of both abnormal and normal strokes is described, in particular in the symmetric case, in relation with observed motions of the microorganisms. Moreover C 1-optimality is studied using the concept of conjugate points, depending upon their respective shapes. In parallel direct and indirect numerical schemes implemented in the Bocop (www.bocop.org, 6) and HamPath softwares (www.hampath.org, 14) allow to perform numerical simulations, crucial to complete theoretical study and to evaluate the optimal solutions.