I'd say this depends entirely on your play style, the issue with a single point sling is if you haven't got a hand on the slinged gun and you start running, it gets a little unwieldy and bounces around, at least with a 2-point sling you can get the gun on your back and out of the way as well as close to the body if you have a quick release/quick tighten 2-point sling.
Single sling works for me normally because my side arm is a pistol which means it's easy to aim as i can use my tricep to hold the slinged gun against my body, might be a little harder when your trying to pump a shotty, you could probably learn to get used to it. It's all trial an error till you find whats comfortable.