Which item is better for a warlock?

[NecroDancer]

Assuming this is your standard blast-lock what item would you attune to?

A periapt of wound closer.

Or

Slippers of spider climb.

The only other items you have are an orb of the war mage (+1), some mundane scale mail, and a mundane shield (from a feat). Your HP is 51 and your AC is 18.

[Ferrin33]

You can get high ground and easily avoid enemies with the slippers, but you become a prime target for ranged enemies. You can more easily use the Darkness + Devil's Sight combo without obstructing your allies, and it will also protect you against the biggest downside that getting out of formation and up high gives; the ranged enemies.

If you have a healer, the Periapt is a relatively minor resource-saving item. Without a healer? Your party members will also need to restore their hit points, and while you can more easily regain them, you would need to wait for them anyway. Unless you get in situations where no one is maxed out on HP, or can afford to rest more, then this item won't add much to the party as a whole. In fact it's an item that's best used by the healer, so they auto-stabilize.

So to summarize; With a healer it's always the slippers, without a healer and without ways to protect yourself from ranged enemies it's a toss-up, and without a healer but with a way to protect yourself from ranged enemies it's a toss-up. That's my take on it.