I have heard, from a doctor, that synthetic saddle coverings will make chaffing worse as they do not absorb moisture leaving it to be soaked up by the shorts and skin, which ultimately dries the skin out leading to increased chaffing. Leather saddles are by far and away the best.
The worst chaffing I ever had was when I had an SDG Bel Air saddle; since then I have only used leather covered Selle Italias. I would say that the only time I do get chaffing is when I am using poor short liners. Having said that, when I go for long rides I do still uses Assos chamois cream, purely to be on the safe side.