Neither cause any wear on my pants pockets, as I take them both of the knives I carry. But, based on observation of the clips themselves, I'd found a fair percentage of the solid ones to have at least a few rough spots along the edge. To me, this would cause wear and tear on clothing unless one took the time and effort to correct it. Given the fact that they are stamped and formed pieces of sheetmetal, the rough edges are not terribly surprising. On the other hand, I've never observed rough edges on a wire clip, and the very nature of wire make me think it less likely, so I'd venture that the wire would have less potential to cause wear, at least straight "out of the box".
Second, strictly "theoretical" observation - it would seem reasonable to say that most of us carry a knife for a considerable amount of time each day, but only remove it from and replace it in the pocket occasionally. Thus a tight fitting clip, while it might cause more wear when the knife is retreived and replaced, may very well save overall wear and tear by preventing the constant rubbing action a more loose fitting one allows when the knife is in the pocket and the user is in motion.
