Okay, I need your general opinion on the matter. What proves more the stronger pertaining to defense stats, Hp or Df/SDf?

Shuckle possesses piss-poor Hp, but his Df/SDf is booming. This goes opposite for Wailord (not regarding approximate calculations/numbers here, mind you).

NOTE: I don't care for these particular Pokemon (well, Shuckle, maybe). They are simply examples to raise a subject.