Mythril Drill

The drill digs faster straight out of the box and then never gets any faster. Speed bonuses from armor, accessories and potions are ignored entirely, so the moment you assemble a proper mining loadout the pickaxe of the same tier pulls ahead and stays there. The drill also reaches a tile less, which sounds like nothing until you are hollowing out a tunnel and have to reposition every few blocks.

Take the drill if you have just crossed into Hardmode with no mining gear and only want the next ore tier unlocked. Take the pickaxe if you build, or if you drink mining potions out of habit. Its counterpart from the alternate ore is a little better across the board, so a world that rolled the other one is not costing you much.