Edit: Completely redid my post as I researched a little bit.
I initially wrote that +Parry would suffer from Diminishing Returns whereas +Defense would not, in complete disagreement with FailureMidgard. After rereading his post I investigated a little bit, and it seems both pure +avoidance stats as well as +Defense both have diminishing returns- thus, Defense would not necessarily be better, as was my initial wager, but it also invalidates a large portion of FailureMidgard's post as well, as +Parry isn't 'better' than +Defense. Read on if interested-
Link for further reading:
Avoidance Diminishing Returns - Elitist Jerks
In other words, the +Parry from the rune will not 'scale' with gear, unless Blizz releases it to be counted differently, which it very well may be- there is no DR on talents, base agility, etc [Gorek]. I do want to agree with what Midgard is saying about comparing item points / ilvl, in a roundabout way... Mostly as per Arcana's post-