I've used both and like the string loop simply because it is lighter and cheaper. I never experienced any of the negatives you hear about the Ultra Nock (I had the XL). Other than it was heavy. I also used a rolleraid release so wear was not a problem.

Now I use a string loop with a release designed for it (small hook on the end with a short head).

I also have a fletch hunter 3-D release if I want to shoot right off the string. It has a larger smoother curve on the jaws so it doesn't damage your string. Kind of a pain with a loop though, hence the new release specifically for the loop.

Paul