Colossus's armor couldn't protect him from Deathbird's acid-like attack, Avalanche, or Pyro's flames when his powers were going haywire when he had the legacy virus. He shouldn't be on the list.
First grade adamantium hasn't proven to be destroyed by regular means and I've never seen Captain America's vibranium shield destroyed. But on the list, I'm leaning towards Silver Surfer skin, as it's hard to imagine that mankind of all the civilizations in the universe could create something more potent than durability by a cosmic.