Blessing of the Lady or Mystic Shield

[whataseamus]

If I'm fielding a Damsel of the Lady with a force of Bretonnian knights, is it better to cast Mystic Shield or Blessing of the Lady? A 2+ save on the charge is pretty impressive, but would a 3+ with a 5+ save against wounds and mortal wounds on top of that be better? I can't quite make the math work in my head to figure out which is statistically better.

[Shorewood]

lets see here against no rend 1/6 of wounds get through your armor using mystic shield.  

With the blessing of the lady 1-((2/3)+(1/3)(1/3)) = 2/9

giving them a common denominator you've got 3/18 wounds getting through with mystic shield and 4/18 getting through with the blessing of the lady.  Now it should be noted that (I assume) the 5+ extra save the blessing of the lady gives is not affected by rend and lets you save vs MW, it'll prove much more effective against rends and MW than mystic shield while mystic shield is slightly better (5.5%) against no rend.  

[Shorewood]

To continue the math against -1 rend

Mystic shield 1/3 wounds get through

Blessing of the lady 1-((1/2)+(1/2)(1/3))=1/3

So against -1 rend they offer equal protection

 

-2 rend

Mystic Shield 1/2 wounds get through

Blessing of the lady 1-((1/3)+(2/3)(1/3))=.44 of wounds get through

So Blessing of the lady pulls ahead by 6%

 

-3 rend

Mystic Shield 2/3 wounds get through

Blessing of the lady 1-((1/6)+(5/6)(1/3))=.55 of wounds get through

So at this point the Blessing of the Lady now has a lead of 11% which is pretty good.

And its only going to get further in the Lady's favor from here on out, not to mention the 5+ against MW that the mystic shield provides no protection against.  

 

Final Conclusion.  Unless you are charging a unit with no rend and are not expected to be hit by MW or rending ranged fire use mystic shield, otherwise the blessing of the lady is the way to go.