IMO a D-loop has many advantages,for one with a D-loop thier is less twisting of the string witch will rob accuracy and buy removing the added weight on your string from the two brass nocks and the groumet,it will give you a little more speed! Also they cause no damage to your serving.
There is a sticky with directions on tying soft nocks and installing a D-loop I do mine a little differant but IMO soft nocks and a Loop are the way to go!