For more detail, see the Weapons section of this guide. It depends. As a general rule, Hamayumi is better in Melt if you use 4pc Wanderer’s Troupe and don’t Burst, while Prototype Crescent is better in all other scenarios.  However, this assumes you can proc Prototype Crescent’s passive. You may find that many enemies don’t have a weak point or that you cannot proc the passive reliably even when they do. In those cases, Hamayumi performs better, even without its passive.  It’s up to you to make the final call; either one is good enough to clear most content. Of course, you could just craft both, but that requires more billets.