Tungsten Helmet

Every world generates either tungsten or silver, never both, so which of the two you end up wearing is decided before you swing a pickaxe. The silver set covers the same slot in the worlds that rolled it, and the two do the same job at the same point in a run.

Wearing the helmet, chainmail and greaves together adds a bonus on top of what the pieces give on their own, so there is no reason to mix one part of it into another outfit once you have the bars for all three.

It is enough armor for surface nights, a first real trip underground, and the Eye of Cthulhu if you build an arena for the fight. It is not enough for the Dungeon or the Underworld, and it starts feeling thin the moment you meet something that hits more than once a second.

Clear one good vein and stop there. Gold or platinum turns up soon after, then the ore from your world evil, and tungsten stockpiled past a full set has nowhere useful to go.