I did the math on my gear which has drastically higher dodge than parry using warloco's formulas.
729 def, 526 dodge, 204 parry
adding 16 of each rating provides,
16 def added = 0.24% avoidance
16 dodge added = 0.23% avoidance
16 parry added = 0.24% avoidance
So you need a pretty extreme difference in your dodge and parry rates for parry to become better, largely due to the much harsher diminishing returns. Oddly enough in my gear I'd have to say that defense would be the best stat for avoidance, since it provides block as well. As others have said though, you really need to run the numbers on your own gear to be certain what works for you.
Course the whole thing is even more amusing to me. After all nerfing avoidance just means that health and bonus armor are just that much more valuable. Going straight blue gems regardless of socket bonus is starting to look attractive in 3.2, particularly considering epic gems.
As of this state of ptr, I'd treat all three avoidance stats roughly equal once your def capped, and stack effective health wherever plausible.

