Gold Bar

Gold is the last of the common early metals and the temptation is to dump the first full stack into armor. Check your timeline first. If the Eye of Cthulhu is already down and you are heading for the jungle or a fresh meteorite, whatever you find there replaces gold gear almost immediately, and you will want those bars back. If you are still scraping by in silver with a boss ahead of you, make the armor and do not think about it again.

What gold is genuinely worth hoarding for is the things with no substitute. A Gold Crown becomes a Slime Crown, which is how you summon King Slime whenever you want instead of waiting for one to wander over. Thrones, candelabras and the rest of the gold furniture line eat bars permanently. If your world rolled platinum instead, the equipment made from it is a touch sturdier, but any recipe that accepts either metal does not care which one you feed it.

The Goblin Tinkerer insisting gold beats iron is a dig at real metallurgy. Actual gold is heavy and soft enough to scratch with something as dull as a coin, which would make for the worst armor in any world.