Sampling circuits (SCs) with internal antialiasing filtering in software defined radios allow significant increase in dynamic range, flexibility, and scale of integration of the analog and mixed signal portions of these radios. Filtering properties of the SCs are determined by their weight functions. While these weight functions can be optimized for filtering according to formal mathematical criteria, these optimal functions may not be useful due to the complexity of their generation. For this reason, it is often preferable to use suboptimal weight functions that simplify the implementation of the SCs. One promising class of suboptimal weight functions is based on B-splines. Comparative analysis of optimal and B-spline-based weight functions is given in this paper.