Palladium Ore

A world generates this or Cobalt Ore, never both, and the decision is locked in the moment you break the first altar. Palladium gear leans on health regeneration triggered by landing hits, which suits a melee character who is going to be in contact with things constantly. If you wanted the other metal, crates, a friend's world or the Chlorophyte Extractinator are the routes across.

A Molten Pickaxe is the entry fee and nothing weaker will scratch it. Standard explosives do nothing to Hardmode ore either, so blasting a vein open is off the table apart from the Power Bomb line. The orange stands out against cavern stone better than most ores, so you can get away without a spelunker effect more often here than you can hunting cobalt.

There is no gain from smelting before you sell. Raw ore and finished bars come out to the same money, so dump whatever form the surplus is already in and keep the furnace free for something you actually intend to use.