Platinum Crown

It is filed as vanity, but almost nobody smelts one for the look. The crown goes into a Slime Crown, which is how you call King Slime at a time and place you picked instead of waiting on a random spawn or grinding a Slime Rain to its end.

Crafting the summon consumes the crown, so if you want to wear one as well, budget for a second. The gold version behaves identically for every purpose, so whichever ore your world generated is the right one and there is no reason to hunt for the other.