Internet predominant transport protocols, such as TCP and TFRC, face degradation of their performance in Multihop Wireless Networks because of their high loss and link failure rates. Many solutions have been proposed to improve the transport layer operation. These solutions are either based on network state estimation or use information from MAC layer (called MAC metrics) in a cross-layer manner to better comprehend the network state. In this paper, we define a new MAC metric called Medium Access Delay (MAD) to better reflect the network state, and provide a comparative study of MAD over other pertinent MAC metrics, their expected usage and measurement methods at MAC layer. We also investigate the behaviors of MAC metrics through several experiments in order to reveal their effectiveness in reflecting network events such as contention, collision and losse.