I've used a few diffrent ones. Honestly one of the ones that worked the best for me was a rigged issue service sling like how I have it setup below.
550 Cord around where the delta ring normally is and the other end strapped around the buttstock. Works good for me and is free since I can get those slings.
I also have used 3 point slings which work okay but the extra sling piece running across the rifle can get fouled in your gear if that is a concern for you or not.
I have yet to use any single point slings but I hear good things about those for a lot of people it's personal prefrence. The sling I rigged above works well for me and is very cheap.
Here is a sling I found on CTD website that will probably work for you.
http://www.cheaperthandirt.com/ARR103-44883-2699.html
This one will work if you have a 20" model this may not work for the shorter ones. Too much material.
Here is one that will probably work on the shorter model ARs
Here is their tactical sling page
http://www.cheaperthandirt.com/tactical_bbfj.htm