These two are winners.

Gridanian Square Shield:
68 Block Rate
46 Block
+10 Magic Accuracy

Gridanian Staff
+20 Magic Accuracy
+20 Magic Critical Rate

As said before, you can't materia Crit Rate, making the staff a worthwhile and +20 M.Acc is nothing to sneeze at. I like the shield the most, +10 M.Acc on a shield is awesome and I wish I could put on up. I think you can never have too much M.Acc.