My main gripe with the Defender is that the phone is surrounded by hard plastic and then silicone. I would much rather the opposite, so that the softer material (silicone) touches the actual phone.
I had a Defender for my iPhone 6. It did leave several small scuffs and dings on the front of the phone by the home button and speaker. Not to mention that it impairs TouchID and the area between the screen and screen protector is a magnet for dust. I've sworn off the Otterbox Defender. They are a waste of money, bulky and ugly.
A speck CandyShell or MightyShell and a screen protector will be just as good as a Defender for drop protection. If you want dust or water resistance, get a LifeProof case.
It's also worth mentioning that the screens on the 6 and 6s aren't as scratch resistant compared to the 5s.