Mohair string cinches, not too narrow, lots of strands. 100% wool or mohair for the 'give' because western do not have elastic like english girths do. I avoid nylon or blends. I hear Alpaca wool is great.
I avoid neoprene or non-slip material because the cinch does need to move during tightening and I feel it would pull or pinch or tear a few hairs out during the process. Plus I had a mare that let me know that.
I do have one that is nylon webbing backed with wool felt, another backed with sheepskin. I like those for winter because the backing goes up past the ring so the cold metal doesn't touch the horse.
I like neoprene. They fit my horses well and they don't pinch. So far I have not experience any galling on my horses. They are very easy to clean. Currently, I'm trying the Weaver Airflow cinch with double rollers.