Well they both do different things. Dexterity is imo generally more important, as it allows you to start aiming and firing sooner after sprinting, and most people like to sprint around a lot. Quickdraw reduces the time it takes for you to aim down sights. Dexterity also allows you to climb faster, which is useful.
Mathematically ARs do get a very strong boost from Quickdraw, but personally, Stock is mandatory for all ARs. As such, almost all of my ARs use Stock and Fast Mags. If I need a silencer, I will use Primary Gunfighter.
On the other hand, Dexterity is on every single class I use. Personally, if you desperately want Quickdraw, I'd use both, otherwise just use Dexterity. If it were me, I'd drop the equipment and go Primary Gunfighter and get everything. --- PSN: Toastie88 | XBL: ARGH ZUBATS | Steam: webbc99 Playing: MH3U, Call of Duty: Black Ops 2, World of Warcraft