Beamforming with a spherical microphone array has become an attractive tool for sound source localization in cabin environments. To provide a reliable localization solution with high performance , the first step is to optimize the array design. In this paper, the spatial resolution and dynamic range of an open spherical array with various microphone arrangements are evaluated, which are used as metrics for optimal array design. Several popular approaches for evenly distributing points on a sphere are investigated such that the array response is as isotropic as possible. In addition to the conventional beamforming, a state-of-the-art algorithm called functional beam-forming is also implemented. The objective is twofold: first is to improve spatial resolution and dynamic range significantly; and second is to verify that array configurations have a consistent effect on localization performance, regardless of beamforming algorithms.