The SS model uses a sapphire face so it is pretty scratch resistant. Unless you intentionally scrach it with a diamond ring. Early last year a guy did that just for a YT video.
My wife is not rough with her sport and it has no scratches. The sport uses that hard glass face, which is not considered scratch resistant.
I posted some ideas for a more dressy looking case protector than the cheap plastic ones. I have an 18K Gold plated one and a black SS anodized one. They are really low cost, snap on easily and with the same style band you can dress up your watch as a Gold or Black SS, or Rose Gold for between $35 and $50. My wife puts on the Rose Gold case cover and band when dressing up.
http://www.amazon.com/s/?ie=UTF8&keywords=apple+watch+gold+cover&tag=satell01-20