Scarce bandwidth and interferences in mobile ad-hoc networks yield the need for more efficient diffusion techniques than these employed on usual wired networks, especially in dense environments. In this paper, we compare some optimized flooding mechanisms that were proposed in view to gain enough performance and allow applications such as multimedia diffusion in an ad hoc environment. We namely present multi-point relay (MPR) flooding and gateway flooding. We investigate the matter theoretically via mathematical modelling, as well as practically via simulations. It is shown how well each of these techniques improve the diffusion performances: when the network is dense, 2/3 of the gateway nodes participate in the retransmissions, while the density of multi-point relay retransmitters is 1/ν , where ν is the node density.