I shot a 5 pin for years but have dropped down to a 3 pin now set at 20, 30, and 40 yards. Never take shots farther than that in the thick woods here in Alabama anyway.
I guess the advantage/disadvantages of both would be this.
Multi Pin Bad: A multi pin sight I guess blocks a little more of your view although I've never had it be a problem for me. There also exists the possibility that you might inadvertently aim with the wrong pin in the heat of the moment.
Multi Pin Good: There are multi pin set ups out there from 3 up to 7 pins if you like. If you count the gaps between them too that gives you about as many aiming points as you could possibly need for any hunting situation. And you don't have to make any adjustments come shot time.
Single pin Bad: A single pin will either be fixed or a slider type adjustable. With a fixed you are gonna have to remember to aim at different levels on the deer for various distances. And IMHO you are just as likely to forget to aim at the right spot as your are to use the wrong pin with a multi pin sight. So I see no advantage there. With a slider you are gonna have to possibly make adjustments just before the shot. Where I hunt the woods are thick and shot opportunities can pop up quick and be gone just as fast. I personally do not want to have to be making adjustments to my sight at such a time.
Single Pin Good: No possibility of aiming with the wrong pin. Less obstructed view. Just aesthetically more appealing to some folks.