The defender is he godfather of all cases. It has what Otterbox calls 3 layers of protection. It starts with a hard plastic case. It comes apart into 2 pieces and snaps together. This is what the phone goes into. This hard plastic case also has a built in screen protector. Its a thin piece of clear plastic that is build in to the hard case. It in NO WAY affects how the screen operates. Though it does affect how the screen feels. It feels like a resistive touch screen with the case on. Then on top of the hard case goes a silicone case. There are tabs on the hard case that align the silicone and hold in in place. It is the best silicone case I have ever had. It slides in and out of your pocket very easily and doesn't hardly attract lint.
I have a defender on my ipod touch and it is AWESOME. When Otterbox says it provides the best resistance from shock, bumps, and damage, they mean it. I don't know about the commuter case but I would go with the Defender. Now, this case will add some thickness to the phone, but I think thats a small trade off for the protection that it adds. I tend to drop things so this added thickness has helped me.
BTW, thanks for posting this. I've been waiting FOREVER for this case.
Edit: Just checked Otterbox's website, the Defender series is NOT available yet. I repeat, Defender is NOT available yet. I also looked an amazon.com, they said the cases will ship in 3 - 5 weeks.