Another on the vest, you can still reach all the mag pouches and shoulder the rifle to your strong and weak sides. The only downside I found was I had to give up my admin panel.
It`s faster that a dropleg too. Picture your weapon at your shoulder and it stops firing. Presuming you have a proper sling and not some sort of jimmy jack elastic it falls away and you just bring your right hand straight to the butt of the pistol and draw. Of course if you shamble along with your arms dangling like a chimp the dropleg could work.