I prefer the metal clips. They will scratch the gunbelt slightly over time, but they're always in the same place so it's not noticeable.
99% of the time, I carry a horsehide White Hat. However, once in a while it needs a "drying out" day, and I have a "Cozy Partner" with leather loops. I've found that the loops allow the holster a bit more "freedom" than I really like during a draw...when compared to the metal. Of course, the Cozy Partner is all leather and the White Hat is leather/kydex...that may be the real difference.