I use quickdraw for weapons that are going to be in CQB, ARs like the MTAR and the Type 25 are great with the quickdraw because it means that their ADS time is halfed, add Dexterity and you will not have much problems when you are sprinting and an enemy appers. LMGs need the attachment because of the suggishnes they have. It only gives them a third of their ADS time cut, but in a fast-pace game with a slower handling weapon any way speed up the weapon is good.
Every attachment, except the grip, has a good use for it. You just need to know your playstyle and see if the attachment will help you.