This paper reports the results of a simulation comparing the performance of the following wavefront sensors when used in a closed loop astronomical adaptive optics (AO) system: a 48- element Shack-Hartmann, a 20-element Shack-Hartmann, and a 20-element curvature sensor. The method chosen for wavefront reconstruction in each case is based on a modal interaction matrix technique with zernike polynomials chosen as the basis modes. No attempt is made to include a real mirror model in the simulation, thus the evaluation of the sensing technique is decoupled from specific mirror technologies. Two different seeing conditions are simulated with various guide star magnitudes. The wavefront distortions are sensed in the visible and the point spread function of the corrected wavefront is recorded in the near infra-red. The effects of photon statistics and various levels of sensor pixel readout noise are also included in the simulations.