Based on the results of electron optical simulations, we report on a comparison of the performance of stigmatically focusing magnetic prisms designed with two different symmetries. One type consists of a set of square inner pole pieces surrounded with rectangular outer pole pieces, which is similar to the magnetic prism in Tromp's design [R. M. Tromp et al., Surf. Rev. Lett. 5, 1189 (1995)]. The other type consists of a set of nested round inner and outer pole pieces, which is similar to the magnetic prism we constructed for our low energy electron microscope [H. C. Kan, D. Auerbach, and R. J. Phaneuf, Rev. Sci. Instrum. (submitted)]. One interesting difference is that the square pole piece prism produces a strong linear dependence of the focal point position on the impact parameter in the deflection dimension, compared to what is seen in the performance of round pole pieces. This linear dependence produces asymmetric distortion in the imaging in the deflection dimension.