While I believe that there can be many changes to weapons in this game and some weapons are fairly balanced, My vote would go to the manmelter. Why the manmelter? Well for starters, it is by far the least used pyro secondary. While it's ownage percentage is roughly 72%, It has an equip rate of roughly 4%. The only lesser used secondary for pyro is the limited festive flare gun, which is just a limited time reskin. This low equip percentage is most likely due to the fact that people running this are only running the phlog, as they are meant to be combo weapons along with the third degree (entirely new analysis needed for this). The problem is, aside from the phlog taking roughly 13% usage of all flamethrowers, is that some phlog pyros only run it to extinguish teammates. That's it. Even then, most phlog pyros run the thermal thruster or another secondary that either gives the pyro mobility or more range, like the shotgun. The no ammo required isn't all that helpful, as ammo packs are plentiful and some pyros, like me, don't run out of flare gun ammo. The 50% projectile speed is the only really good aspect of this weapon, as flare guns can be easy to dodge from a long range. The no random crits is pretty basic, and the alt-fire can give crits for extinguishing teammates, its still only if you extinguish teammates. Due to low versatility and low usage, the manmelter gets my vote. Of course, the analysis part is opinionated so there can be others who disagree with me. which is completely understandable. I think my last input would be a possible buff. Personally, I think that it should have some kind of bison mechanic, where it can pass through enemies and light multiple on fire to help clear choke points, but that's just my input.