depends on build but you want

positive/material/opposition ~ unconc range and passive heal
negative/material/opposition ~ saves augment slots by giving deathblock, blindness immunity, and fear immunity

x/material/opposition ~ for your least favorite element you take damage from. It's only going to have like 4% effectiveness in hard content but its worth a momentary thought.

I would go for necklace, since its mostly a dead slot atm. Helmet you eventually want reaper bonus. Gloves are off limits for casters/melee but they're good as a third slot for tanks. Cloak is always nice as a swap slot on almost any toon. You will need spell absorb anyway at some point.