So far I've been using a mix of Armor and +Str talismans. The extra strength gives a bit of parry & block strike through which it more important than armor penetration IMHO for a shield dok. As if you get blocked or parried you don't even get the base healing value.
Also Oppressor/Dominator + Beastlord gear combinations give very little initiative, and the DoK has very low base initiative compared to most classes. So with that gear combination you might need one or two +Ini talismans even. Otherwise you will sit at ~180 initiative, and if you get an intitive debuff you will suddenly have like 50% chance to be crit.