Prospector Pants

This is digging gear. The bonus speeds up your pickaxe, which sounds minor until you are sinking a shaft to the underworld or clearing a marble cave, where every swing saved adds up over an hour. The set also gives off a faint light of its own, enough to keep moving through an unlit tunnel without stopping to place torches every few blocks. What it will not do is help you fight. There is no damage bonus attached anywhere on it.

Pieces mix freely with Mining Helmet, Mining Shirt and Mining Pants, and with the Ultrabright Helmet, and the bonus still fires either way. So the only real choice is which head piece you put on. The Prospector one is the tougher option. The Ultrabright version gives that up in exchange for the vision effect it inherits from the Night Vision Helmet, which genuinely makes dark caves easier to read. Tunneling through Hardmode spawns, take the Prospector. Exploring rather than digging, take the light.

Its protection sits in the range of the early Hardmode ore sets, so being jumped underground in it is survivable, but change back into a class set before you summon anything. Worth knowing if you are planning ahead: the Ultrabright route opens up earlier, because the helmet it upgrades from comes off enemies that already exist before Hardmode.