u/Dya_Ria

I was doing some testing with shields since sword and board is my favourite way to play most games and I've found some interesting results. All of these were tested against Marni's Excavatron, since it has an underground multi attack, as well as much more powerful one that does a ton of stamina damage, pretty much guaranteed to break the guard of anyone who uses shields casually. From my findings I've concluded a few things:

• Upgrading your shield vastly reduces how much stamina damage you take.
• Shields categorized as Large Shields block much better.. My upgraded large shield
• can block the Excavatron's most powerful attack, and it's regular attacks did so little stamina damage that my stamina bar flashed for maybe 1 frame before it was full again.
• There's no difference in stamina recovery speed if you're blocking or not, in case Dark Souls taught you lower your shield to regen stamina faster.
• The difference between the large shields is neglible. Use whatever you want.
• A fully upgraded normal shield, as well as Damaine's shields, is only slightly better than an unupgraded large shield.
• The Abyss gear that reduces stamina cost by -9% (Fortitude) does work but is also neglible.
• Shields can also parry attacks with their shield bash. It must be done while holding block before the enemy's attack hits you. Similiar to parries in Dark Souls 1. Large shields have a smaller window for both kinds of parries though.
• You can do a short ranged tackle after a shield bash, as well as the longer normal charged one. Both have instantly active block frames.
• Normal shields regen stamina faster, but have a longer delay before stamina starts to regen. Large shields have a very short, if not non-existant, delay
• Large shields paired with a sword can attack safely from behind the shield. I was 100% safe during the Excavatron fight, on hard mode, with the stronger rematch version. As long as you have the stamina for it, bosses can't hurt you outside of small amounts of chip damage. That's right, Elden Ring shield poke meta is back
• Shields can also follow up with an Elden Ring style guard counter after blocking an attack. The animation is different between both kinds of shields, and the large shield's version does more knockback. However, both can only be done with a sword

TLDR. Upgrade your shield to block better. Use a large shield if you want to safely turtle or a normal shield if you want to be more aggressive with parries. Use your shield charge escape getting swarmed by enemies if parrying is too hard for you. It was for me.

There's probably a lot more to shields than just that but that's what I've observed so far.