Wilderness Single Point Sling on all shotguns and AR15s.
Why ?
Well, it was recommended to me by someone who I consider an authority on AR15s. I used them on AR15s for a year or two and when I decided I wanted a sling on my shotguns I decided that it would only make sense to get the same sling.
I have used these slings in a total of six, five day classes and am plenty satisfied with them. I do see some drawbacks though depending on what you are going to do with the gun. If you simply want a tactical sling, then the Wilderness Single Point Sling would be my choice. If you were going to be hunting with the shotgun, or using it in anyway that you didn't always want the shotgun ready for instant use, then the single point sling becomes a PITA. An example might be trying to drag a deer out of the woods. Here having a conventional sling makes sense.
Like a lot of gun owners, I occasionally let myself slip into the fantasy world of SHTF/TEOTHAWKI. It occured to me that there might be times you might want to attach the carbine or shotgun to your backpack frame or something. This would be a lot easier with a conventional sling. However, there is nothing stopping you from having sling swivels on the gun and simply using a conventional sling if you needed one.
In gun skool, there is nothing that even comes close to the single point sling IMO. Not having a tactical sling in skool is a major strain on your back and arms. Same goes for anytime you would want to walk around with your gun ready for instant use.