Molten Pickaxe

The swing is slow, and that matters more than the power number suggests. Through dirt, mud and sand a Bone Pickaxe clears ground faster simply because it swings so much quicker. On stone and anything harder the Molten wins outright, and it is the tool that gets you into the Dungeon and through the first tier of Hardmode ore.

It also glows while you swing it, which is enough light to see the next few blocks in an unlit tunnel and saves a torch on the way down.

Reforge it for what you plan to do. Speed modifiers make it a digging tool, damage modifiers make it a passable early weapon that sets things on fire on the way past. You cannot have both, and in practice almost nobody swings this at enemies once they have a real sword.