The wider the pad the less it will dig into your shoulder on a long trek.
However a wide thickly padded sling is tough to wrap around your fore arm for steadying your off hand while aiming.
Rubber backing keeps the sling in place removing the necessity of repositioning it every 5 minutes, but it gets stuck in place some times not wanting to come off your shoulder when you want it to.
Suede is a good compromise between stick and slip but the down side is it doesn't like being wet.
Choices abound.