The implementation of energy-maximizing control systems (EMCSs) can significantly increase the efficiency and economic viability of resonant wave-energy converters (WECs). To achieve optimal control and drive the WEC into resonance with the incoming wave field, knowledge of the wave excitation force is required. In operational conditions, this quantity is immeasurable and, thus, has to be estimated. This article presents a critical comparison of the available excitation force estimators found in the literature. A reference measurement of the excitation force is determined using computational fluid dynamics (CFD) simulation, allowing an absolute comparison of the different estimation strategies. The estimators are compared based on the required input data, achieved accuracy, computational delay, and estimation time. In total, 11 estimation strategies are compared, with three, in particular, emerging with relatively superior performance.