Constant Effect
I personally prefer armor and weapons with constant effect enchantments. Even if the AC is a little lower, the enchantment usually makes up for it.
So I would vote for Saviour's Hide. That being said, I haven't come across the Ebony Mail yet.
Ideally, I'd like to enchant the best piece of armor myself. Unfortunately, most items can't hold enough enchantment points for the types of items you find in the game.