This paper presents an realistic comparison of several electromagnetic architectures forhigh force density actuators. Firstly a simple classification of synchronous actuators is presented. Four equivalent architectures are chosen and modelized by saturable reluctance schemes. For each size and each architecture, dimensions are optimized in order to maximize the force-volume ratio. This optimization is done with fixed mecanical airgap. A simple thermical model is used. Results shows that the optimal number of airgaps increase with the dimensions. Moreover, Global coil architecture performances increase faster than other architectures. Several examples of global coil multiairgaps actuators are presented in order to illustrated the theoretical result.