I agree with Elsie.
Frankly, Dodge rating gives you dodge, nothing else. It does not scale with buffs (ie kings)
Agi is a viable alternative and has been ignored in this analysis.
Does Agi provide as much pure avoidance as dodge rating, on a point by point basis? No...
But it does provide improved mitigation and crit rating.
Basically, 300 dodge rating will provide about .9% more avoidance than 300 Agi will...
But the 300 agi will add about .8% more pure mitigation than the dodge rating will...and it will add about 6% to melee crit.
Tanking is about more than just pure avoidance...its also about threat.
Dodge rating as a stat, simply gets us to high DR faster than agi does.
Now, if we are purely looking at just avoidance, dodge does win...
Nothing however, excuses you from having included the new agility enchant to the back item
http://www.wowhead.com/?item=44457
Technically, it provides more pure avoidance than the Titansteel Enchant once kings in factored in.
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Garath Lvl 80 Paladin, Gorefiend