I got my hands on a couple of Facepunchers to carry out some testing. Although I wasn’t using an actual melee build or loadout, I found that the Stinger shield (one of the new ones that drops from Anathema in the Guardian Takedown) was giving me higher numbers than the Rerouter. But that could be because it was my only source of bonus melee damage at the time. Once I get more appropriate gear to make a build with it, I’ll test the numbers again.
I’m not sure if the Stinger can drop with amp parts. But I would think that it should considering that it is a Pangolin shield. If it does then it would absolutely be the best shield for a melee Moze, assuming that the amp’s shield-draining effect doesn’t negate the bonus melee damage.