During preview weekend I typically kept the Oath Rune of Warding on myself. I was surprised to see on these boards that many (maybe even most) favor self-buffing with the Oath Rune of Iron.
To be sure I wasn't completely nuts, I decided to run some numbers and
compare the benefits from each. I looked at each oath rune under ideal
conditions - i.e., with the given mastery path maxed out. Your mileage
will obviously vary based on what spec you choose.
With 15 mastery points in Grimnir, Oath Rune of Warding gives an
additional 14.95% mitigation to all damage types. That's some serious
business, at least as long as it's not dispelled. That's compared with
80 willpower and initiative on the Oath Rune of Iron.
At level 40, with Valaya maxed out, Oath Rune of Iron gives us:
1.71% chance to evade ranged attacks
1.71% chance to disrupt spell attacks
+18 healing per second
In other words, we get around half of what the tactic Discipline gives
us, plus a little bit of evasion gravy. Oath Rune of Iron is worth a
little more than half of a tactic.
With Grimnir maxed out, Oath Rune of Warding gives us:
14.95% mitigation to corporeal damage
14.95% mitigation to spiritual damage
14.95% mitigation to elemental damage
In other words, Warding gives us the effect of the tactic Stubborness,
plus the same effect applied to two other damage types. The rune is
roughly equivalent in value to 3 tactics.
Now I'm all for willpower stacking, and plan on speccing as heavily as
possible into willpower with my renown points and on using Discipline,
but it seems to me that that's a huge tradeoff in terms of value, and
that I should not hesitate to trade the potential extra stats from Iron
for the increased mitigation from Warding. And I fully acknowledge that
avoidance is far better than mitigation, especially since some of the
things that can be avoided are debuffs that mitigation won't help
against at all. But when you're looking at a choice between a certain
amount of avoidance and almost 10 times that much evasion, the evasion
looks like it will have a much bigger impact.
Even if you have no points in Grimnir, you get 9.4% mitigation to the
three non-physical damage types; I'd still take that over the
max-Valaya'ed Iron. But since I'm planning on speccing up Grimnir, it
seems like a no-brainer: as best I can tell, when compared with similar
tactics available to Rune Priests, the effect of the Oath Rune of
Warding are objectively far superior to the effects of the Oath Rune of
Iron.