Cat among the pigeons here... I would say, totally subjectively, the difference for me between leather and rubber (given there are many different types of both), is that leather has a natural warmth that rubber lacks. Rubber definitely creates a harsher sensation than leather, and I'm specifically thinking about flat sheet rubber, not the pink spaghettini stuff, but it also has a more impersonal feel, an indifference to the skin that I don't feel with leather, even pretty hard leathers. For example, rubber doesn't caress the skin like leather does - maybe because leather *is* skin, while rubber is extruded in vats in some hideous chemical alley. It seems to me that rubber creates a distance between the top and bottom, whereas leather is more connective, and depending on where and what you want to play, you would choose one or the other.