I have shotwith a string loop, a metalloop andoff the string. The string loop is by far the best way to go IMHO.

No serving wear like you get when shooting off the string. THe loop weighs less then either the brass nock or metal loop, no release wear like you can get with the metal loop, no screws to work loose, Very easy to adjust up and down the string for fine tuning, very easy to replace when getting worn, easy to see when it needs replacing, release pulls from directly behind the string utilizing all of the bows stored energy unlike when you hook directly to the string (the bows string under the arrow instantly has slack and snatches the arrow downward as the cam rotates foward when you hook up to the string), and a bunch of other benefits.