I did have skin for my SPRO1, but really wanted a case to wrap around it. So I went with the UAG for my SPRO3. Also got the UAG cases for my HTC One WP and my work phone, Galaxy S5. Both look very nice.
I have seen no skins for the S3 yet. A grippy silicone skin would be nice since the naked S3 feels slippery. However, I still have concerns about the fanless, ventless S3 overheating if there is any kind of cover on it that doesn't allow normal heat escape through the case.