Which Shield To Use

[Starsmuck]

I have currently the shield from Nightbane
Shield of Impenetrable Darkness - Items - World of Warcraft (http://www.wowhead.com/?item=28606)

But wasn't sure if the shield from Gruul's would be better.
Aldori Legacy Defender - Items - World of Warcraft (http://www.wowhead.com/?item=28825)

What I most worried about is I lose block value. Is that to much to lose to gain some armor,block,health and some hit rating? Im not to worried about the defense. But I love using shield block and it critting for 1k+. Helps me with threat. I mainly run kara along with gruul's, and mags. And if both would be could when to use what? Thanks!

Also wouldnt mind any thoughts on what to improve on my gear.
The World of Warcraft Armory (http://www.wowarmory.com/character-sheet.xml?r=Icecrown&n=Starsmuck)
Link to my armory but its not showing the new ring I just got from the badge vendor.

[Fitzish]

You lose 18 block value, you gain 15 hit rating, a bunch of stamina and armor. It's a no-brainer to me... aldori is clearly the better choice.

[Crommi]

Aldori Legacy Defender is way better, but it might take a while before you get it. I for once have never seen it drop and none of the warriors in my guild have it. All prot tanks still running with Shield of Impenetrable Darkness, funny enough our fury warrior has Bulwark of the Amani Empire from ZA pug.

[Starsmuck]

Alright thanks.