Leather feels better in hand definitely!
Durability? Only black will stay looking new for long. Lighter colors will show soiling. Some of this can be cleaned with saddle soap. Think of a light colored pair of gloves...
The silicone case OTOH, feels kind of weird, almost sterile. Some with OCD may not want to even touch it! It shows oils from our hands instantly, more so if you hold it after eating greasy foods, etc. That is remedied quickly with a microfiber towelette and perhaps some 70% rubbing alcohol. Silicone will probably last longer in the long run particularly if used in a gripping type belt clip or if the device is dropped a fair amount. Leather wears naturally but the skin is thin and on the edges will tear if abraded from a drop to concrete, etc. That can look rather bad.