My favorite suit of armor is Erdrick's equipment from Dragon Warrior I-III. The Armor of Radiance and Shield of Kings reduces Fire/Ice breath and magic damage greatly, to the point where weaker spells have *no* effect at all. I don't know how well it would hold up against bullets, though...
for me, no doubt about the world renown Mario's overalls. Although here is a question of the ages. We've seen Mario be an exterminator for fire-breathing turtles, we've seen him as a doctor, and seen him as a Gradn Prix racer, but does this "lumber" even, well, is he even qualified for plumbing?
Anything I can't customize is my "least favorite".
But right now, my top favorite is the Ranger Combat Armor from Fallout New Vegas. For those who don't know, it's the cover-art armor, and pretty much unobtainable until a certain level and a certain part of the game and not without stealth-killing the users.
Going to have to go with Fire Emblem's Black Night armor. You're talking about Morrowind and Oblivion's "massive" daedric armor or Dragonage's King Cailan Armor being massive...this is massive!