The Defender Series, as the name implies, focuses more on the protection of your Droid RAZR in the sense that it features a built-in screen protector, a polycarbonate frame and shock absorbing silicone skin, and even comes with a belt clip if you’d rather not carrying the phone in your pants pocket.
The Commuter Series on the other hand will feature a slimmer profile, which probably doesn’t make it as tough and rugged as the Defender Series, but will feature a shock absorbing silicone mid-layer with a custom-molded polycarbonate shell. The Defender Series will cost $49.95, while the Commuter Series will set you back $34.95.