I've had an Otterbox Defender on my 5S since getting the phone last November. The case is fine and I like the fact that it adds a bit of bulk to the phone and is a bit less slippery. I've accidentally dropped the phone in the case at least a half dozen times, and on hard surfaces, with no breakage.
The only part of the Defender I don't like is the screen protector. It scratches fairly easily, but under most circumstances these surface scratches are not noticeable. Got an iPhone for my wife, and she wanted a Defender case, too. She tosses the phone in her pocketbook where all manner of objects live, including sharp ones, and so far, no problems.
I took the case off the phone a few weeks ago...the 5s still looks brand new.