The Shield of Solitude has a unique Magic Resistance Enchantment that you can stack with the regular on with Extra Effect. With Elemental Protection, you can actually exceed the cap, even as a non-Breton. It takes up a lot of slots you could use for something else, though.
The Shield of Ysgrammor is ginormus, so probably second to the Imperial Kites for Deflect Arrows, and Fortifies Block with up to 30%Magic Resistance. This makes it another good choice for maximum protection, but it's still not as good as the Targe. That's Bleeding damage, combined with Deadly Bash makes it a decent weapon. I have entire builds around it as the only weapon, or at least the melee sidearm. A combo with that, and either Fire (Wall of Flames/cloak) and/or Hack&Slash stacks up to significant DoT, so they keep dieing while you're turtled up, and stunlocking them with bashes. It's a slow combat stile, but relentless, and there's not much that can hurt you. (Doesn't work very well on Flame Atronach, because they don't bleed, and are immune to Fire, though.) For the ultimate, Flame Cloak, Ebony Mail, Ancestor's Wrath, an Ebony War Axe of Burning/Firey Soul Trap, and Storn Lingering Poison. If it bleeds, you can kill it, rather quickly, in fact.