The Crown. Lord Stone+Atronach Stone makes for some pretty ridiculous magic defense.
Yes.
Lord's Stone and Steed Stone are the only useful ones unless you are a 'glitcher' and used glitches to up your defs.
Incorrect, that's your opinion. I am invincible against all mages, and I use no glitching, cheating, or that joke of a "skill" called enchanting(no perks).
Atronach, Lady, Serpent, and shadow are all massively useful for almost any character. Absorbing almost all magic, having quicker regen for magic and health, paralyzing someone, and turning invisible are awesome abilities
ALL great examples. Not to mention up to at least 35% skill increase rate boost.
25% Resist Magicka from being a Breton. Lord's Stone's 25% Resist Magicka. + 30% Resist Magicka from Alteration Perks. 80% Resist Magic pretty much makes most spells pathetic... Actually, Legendary Dragon's attacks will only do 100-150 damage. Not much since I can heal like 83, I think, points at a time. Double that when duel-wielding
Even better: My Vampire Lady Archmage wears her robes with her Legendary Aetherium Crown, and is completely invulnerable to magic with the benefit of the Lord Stone+Atronach Stone+Alteration perks+Necromage. Somewhere around 130% magic resist/absorption combo. Now I truly feel like I deserve to be the Archmage, and my secret weapon is my Aetherium Crown. Best RP ever, and I truly feel like I own a legendary artifact now, because even the Daedric ones are kinda pathetic, with the exception of a couple.
You also end up absorbing 100% of summons and perks like Shadow Warrior and Quick Reflexes. And with 80% Magic resist and armor cap you barely take damage anyway.
Not true for summons. I only "absorb" 3/5 summons on average with a similar build. Also, I don't wear armor, but being invulnerable to mages, dragon breath, etc. is extremely awesome for my Vampire Archmage.