The position of the optical beam on an optical detector array is an important parameter for optimal decoding in free-space optical communication systems; thus, its accurate estimation is essential. In this paper, the performance of three estimators (maximum likelihood, center of gravity, and template matching) for the estimation of center of the beam on a detector array is compared in terms of mean square error and complexity. Simulation results show that the maximum likelihood estimate achieves the lowest mean square error and especially performs significantly better than center of gravity under poor signal-to-noise ratio conditions, for both the continuous and discrete/quantized arrays.