Return of Reckoning

Which Ring from skaven quest for dps DOK and which for heal DOK

Parry for dps dok, Reduced crit for heal.

why parry and not reduce crit for both builds?

if you are in melee, parry is more helpful. Parry means the attack misses, reduced crit means you got hit, but there is a slightly lesser chance that they will get bonus damage.

The math of it works out that parry adds far more to defence. If you are in melee anyways. In heal mode, you will attempt to exit melee as quickly as possible(preferably), and therefore the crit reduction will help stop you getting spiked.