I know as registered users you don't have access to ENWorld's search function, but google works almost as well. Go to google, put in
armor "damage reduction" site:enworld.org
and it will give you postings that have addressed this subject before. There is a ton of stuff, and the pros and cons of various methods are discussed at length.
I won't quote any of it right now (frankly, I'm not terribly interested in the subject), but I did want to point you in the right direction.