This paper investigates the wave energy conversion performance of floating and submerged heaving vertical-cylinder buoys. Two types of reactive control strategies are evaluated for their effect on energy absorption in irregular waves described by uni-modal spectra. Approximate near-optimal reactive control based on up-wave surface elevation measurement and peak-frequency tuning are compared for performance improvements over constant-damping load. The paper describes time-domain calculations under unconstrained oscillation in long-crested irregular waves for two sets of buoy dimensions. Supporting analysis and frequency-domain calculations suggest that near-optimal control performs considerably better than peak-frequency tuning for the submerged buoys and somewhat better for the floating buoys. The relative contributions of the Froude–Krylov and diffraction force components, and wave radiation properties for the two configurations are found to be important in this context.