The Naxx cloak has highest armor value in the game. With an armor enchant it's a pretty awesome piece for hard physical damage fights.
A lot of the damage in hard mode encounters is not physical, so in a lot of cases, I would choose stamina over armor, but I keep the high armor pieces in my bag for those times when they are useful.
Same with dodge. Sometimes it's great, other times you can't avoid the damage and you are better off with stamina.
Gear for the encounter, and don't throw away your old stuff, it might come in useful again.