I prefer mohair over neoprene. Neoprene tends to hold heat which can façilitate skin/soft tissue breakdown.
Of mohair cinches, I have some that are the wider roper style, and others that are the same width all the way across. I choose based on the placement of the cinch rings/plate on the saddle, the terrain of where we'll be riding, and the shape of the horse.
I keep several lengths on hand, having a couple for even for my personal horse because his girth changes with his work load.