Gear upgrades on Naxx heroic

[Jibou]

Well, I recently came to obtain many gear upgrades from Naxx25, and it's starting to get much less obvious on what to use. For example, I'm currently using the
Heritage - Item - World of Warcraft
necklace, and just gotten Essence of Gossamer - Item - World of Warcraft, Valor Medal of the First War - Item - World of Warcraft and Defender's Code - Item - World of Warcraft.
I'm currently using the first two, but I was thinking of putting in Defender's code instead of the Essence for melee heavy fights fer example.
Thoughts? Tips?

Thank you