When it comes to quality, the desired result depends on your purpose. Generally, you will want to strive for 100% Grade A items to maximize your experience from crafting an item.
However, various quests will set a minimum grade required to advance the quest. You can exceed the grade required but it's not required.
Some items require 100% Grade A to maximize the benefit of the crafted item.
There is a random chance that a 100% Grade A uncommon item can be automatically upgraded to its Superior grade (e.g. if it was upgrade with a rare upgrade recipe).
There is no difference between an A grade quality refine materials (ingot, sheet, bolt, etc.) and an A grade that was made to 100 percent.
However, as someone else said, you want to use A grade refined materials (especially for those attaches) as they can impact the quality of your final product. The attaches go on at the end, so your result will be an average of the attach and the item you just crafted.
Grade A versus PristineEdit
For clarification, pristine is for items like bags, harvesting clothing/tools, etc. When you make those items pristine (i.e. 100 percent quality) the results will be a better item. (For a bag it would be more slots). For these generic things, you always get pristine if you made the item 100%.
For other stuff, however, making an item 100 percent quality doesn't make it better as a rule. It does, however, give you a 1 percent chance for a free upgrade to superior (yellow) quality. Note, you can only use your upgrade recipes (special finishing) to upgrade a blue crafted item, so if you are planning on making the item orange (flawless) then don't push the quality to 100 percent. If you are planning on making it yellow, then definitely push to 100 percent as you might get lucky.
The only way to get a pristine tox ammo case (yellow) by the way, is with the free 1% chance to upgrade, since there's no upgrade recipe for ammo cases. This means it will take on average 100 combines to make one. The first one I ever made took me like 230 combines. The next one was around 30. Mileage will of course vary as the random number generator is fickle.