Platinum Broadsword

This is the heaviest of the ore swords you can build before your first boss, and the knockback is the actual selling point. Being able to shove a Zombie back out of your face mid-swing is worth more in the first few nights than any small difference in raw hitting power.

It is also physically big, so the swing arc covers a chunk of space around you and catches things you did not aim at. That helps a lot when slimes are coming at you from both sides.

It falls off hard the moment boss drops and Jungle gear come into play. Do not sink a reforge into it unless you are deliberately running a long pre-boss stretch. If your world rolled the other ore, the Gold Broadsword fills exactly the same role a step lower.