My main experience with a sling revolves around the two rifle classes I have taken with my AR (other than using the carry strap in the Army). One class was a five day class and the other a four day class, during those classes I got to wear my AR pretty much all day, and also see other sling systems and how they worked. The sling I used is a single point sling from The Wilderness. After completeing both classes, I have to say that I am perfectly happy with my choice and have not seen anything that would cause me to change. I did modify my sling with the use of a Daniel Defense attachment point plate. It is angled down, so that when you are running the charging handle, you don't catch your fingernail on the sling attachment plate.
One guy earlier mentioned hitting himself in the nuts with the rifle on a single point sling. All you have to do is rotate the weapon around to your strong side. If I wanted the rifle out of my way, I rotated it around to my strong side, such as when walking down to check my target from the 200 yard line. I found that I liked having both hands free with the rifle slung. If I was going to keep the rifle in my hands, I have the rifle hanging right in front of me. With the rifle right in front of me, I found that I could rotate the butt so it was pointing straight up and would rest my arms on it when we were being lectured. I found that I could shoot strong side or weak side without making any adjustments to the sling. I found I could shoot offhand, kneeling, squatting, sitting, and prone without making any adjustments to the sling. I found that I could transition from rifle to handgun with no problem when using the single point sling. And, I found that it was comfortable to wear all day. I see no downside to it at all. Many people at these classes were using three point slings, and I didn't see any advantage to it.