When it comes to shields the stat you want to most concern yourself with is the Block rate. Simply because a lot of pld enmity skills (namely wardrum) require you to block an attack before you can use them. So the more often you block, the more enmity you can generate.

That being said, I believe the shield with the highest block rate in the game (168) is the Lv50 Gridanian Buckler which requires you to be a corporal of the Twin Adders. However, this same shield also has +15 evasion on it as well, which you may think is a good thing, however the game calculates evasion before blocks. So if you have high evasion, you'll just evade attacks rather than block them, which means you won't be able to use your enmity skills. So it's a double-edged sword(shield in this case?)