Historically, it's been +18 stamina to shield if you don't need the +defense.
Weapon enchants it really depends if you're running progression or not. For something taxing your survival, I'm still a big fan of Blood Draining. Mongoose isn't bad all-around enchant too. Accuracy (I think) is the preferred threat enchant for pally tanks.
If what I'm reading is correct, Mongoose may go down in value for Paladins when the patch hits. Supposedly, AGI in Cataclysm isn't going to give Armor anymore. So it may not be the best enchant for you pretty soon. You can still go for it, but just realize that the world is turning upside down pretty soon.