I don't really see either bonesaw or wrench is better than each other, just think about it. Since the wrench isn't that fast, but yet it has a small advantage over the bonesaw at crits. While the bonesaw is fast to swing repeatedly, but its crits are not as often as the wrench. In the end it really depends on the player itself, but I would choose the medic any day because of the speed. As a medic, I know that I have enough speed to kill a couple engys before they could even get a crit.