Platinum Chainmail

Platinum is the last ore set before you move on to gear that cares what weapon you use, and outside of molten equipment nothing craftable before Hardmode protects you better. A world rolls platinum or gold, not both, and platinum is the stronger roll, so a platinum world is a quiet head start. The full three pieces eat a lot of ore, which usually means one dedicated mining trip rather than picking it up as you go.

In a Crimson world the choice is closer than the armor values make it look. The Crimson set trades a little defense for health regeneration, and regen between hits often does more for you than flat armor in a long fight where you are being chipped rather than flattened. If your plan is to push straight through the Underworld toward molten gear, platinum needs less setup and takes fewer detours. If you are about to throw yourself at the same boss twenty times, the regeneration usually wins.

Most of the ore armors look like the metal they came from. This one does not. The helmet is much closer in shape to the Ancient Gold Helmet than to anything you dug up to make it.