We started a discussion in the comments to a previous article about Agility gemming versus Dodge gemming. I decided it would make a good topic for a post on Paladin Schmaladin.
I know some of my readers aren't enamored of Paladin Schaladin, so I'll give you the low down. Agility/Stam in Red Slots if the Socket bonus is 9 or 12 Stamina.
It's all based on the math of Theck and others on Maintankadin, but the bottom line result is "Each point of Agility is around 4% more effective at reducing average incoming damage as a point of dodge rating."
This holds true until your raid buffed armor reaches 42k, at which time Dodge takes back over. If you want to check the math behind how this was figured out, you can read the thread.