Take into consideration what perks are on the armor. Can you live without the perks on the armor you want to infuse? Is there more than a 5 point light level difference? What armor attribute (intellect, discipline, strength) do you want/caters to your playstyle? After you've answered these questions, realize this; if you're trying to infuse a piece of gear with over a 5 point light level difference, you're almost guaranteed not to get the full light level you'd try infusing for. Once you've taken all if this into consideration, you can then make your own inference. This is more preference than anything.