I had White Silicone and Navy Leather. Here is my rundown of both:
The silicone I found to be sticky -- as in, when I removed it from my pocket, it took my entire pocket with it and loose change and notes flew everywhere. Also, after time, the silicone peeled off the casing material, within 4 months I'd say, so I would stay away from that.
The leather I loved, it was smooth and had a nice grip. The patina was nice too, but beware on the navy that the patina can make it appear much darker navy (almost black in some lighting) over time.
Next case is likely to be saddle leather.