What proves more the stronger pertaining to defense stats, Hp or Df/SDf?
Def/SpD, until you get around 200 in the stat. After that defense points normally reduce damage by 1 at best, and sometimes make no difference at all. Hence, HP becomes a larger factor at that level and protects against both physical and special attacks. It also may add to Leftovers recovery and aids against the rare set damage attack. However, there are times where you want extreme defenses (either in place of or alongside HP EVs), and the higher defense will also factor in against attack-boosted opponents. You only reduce damage by 1 for every 3-4 stat points when you get up in the 300's in Def/SpD, but that helps like the lower levels if you're up against a 'Zam with 3 Calm Minds up or something. ;/