I just got my SavvySniper QUAD sling and absolutely love it. The adjustable function is super easy to use, and the quality is top notch as each one is made by hand. It also converts from two point to one point, which is nice if you don't know what kind you want. After playing with it, I can say I'll likely never use it in one point configuration but it's nice to have the option.
Savvy Sniper
FYI, I shelled out a bit extra for the "QUAD X Cobra" which includes all aircraft grade aluminum buckles and hardware. It was pricey, but I consider the sling to be the single most important accessory on your rifle. You can put together a backup plan for every other accessory, but if your sling fails you can do nothing with your hands but hold your rifle...
The company has tons of options and each sling is custom made to order based on your size and stature, as well as what attachment points you want to utilize (QD and HK hooks obviously being the most popular).
Warning***Wait time for my sling was just over two weeks...but for what I received it was well worth it.
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But if you want something a little lower priced, check out the 5.11 VTAC. I like the one I have and still use it to provide stability with my precision AR, as well as when coyote hunting. However the looped adjustment on the QUAD sling allows me to loosen or tighten the sizing with only one finger making it very intuitive and really fast....