Guild Wars 2

Why are there two Elegant Backpacks at the top of the list? They are bothare L78 and look the same.

Offensive and Defensive Agony Infusion Slot

How can you tell which is offense and which is defensive before you craft it?
Is one better? I want to try Fractals soon

You can tell which kind of infusion slot it has by hovering over the item icon in the crafting pane (before you craft it). The infusion slot information is close to the bottom of the item description.

When it comes down to it, there is very little difference between offensive and defensive infusion slots. You can buy offensive or defensive infusions from laurel vendors, but they don’t add much of a difference to stats (e.g Mighty Infusion gives +4 power, but can only be applied to items with an offensive infusion slot).

These infusions can be upgraded via mystic forge e.g. basic Mighty Infusion has +4 power, it can be upgraded into an infusion with +5 power and +5 agony resistance (which will be costly due to the amount and type of materials used e.g. 100 powerful blood).

No matter what kind of infusion slot your ascended item has, you can infuse it with a Versatile Simple Infusion which offers +5 agony resistance and is relatively cheap (75 fractal relics, which you would get after two runs of a low level fractal). This is what I recommend adding to your back-piece.

But to properly answer your question… it doesn’t really matter if you choose an item with an offensive or defensive slot.

I would say that for ascended gear, an offensive slotted item would be slightly better, if you decided to add an upgraded Mighty infusion to it… however because we’re currently talking about only a level 78 exotic it wouldn’t be worth the waste of materials, so it wouldn’t really matter what you choose for this exotic.

I hope that makes sense!

As to how to tell, just mouse over the item in the crafting window. Not the recipe list to the left, the actual icon of the finished item in the right. You’ll see the stats, including the infusion slots. It works that way for any crafted item. You can even link the finished item in chat without making it first (useful for RP’d picnics, I must say).