We present general optimization arguments for resonator-based all-optical switching. Several generic resonator geometries, namely Fabry-Perot resonators, circular gratings as well as micro-ring resonators, are discussed and their particular features highlighted. We establish analytical models which allow a direct comparison of the different all-optical switch geometries. For the parameter range investigated, we find a clear advantage of photonic band-gap resonators (based on Bragg-type reflection) over micro-ring resonators (based on total internal reflection).