I am extremely clumsy. (I once went with a friend to look at engagement rings for his fiancee, and I accidentally flung the diamond we were looking at across the jeweler's store.) I have had Otterbox cases on my previous 2 devices and they were perfect for me - I accidentally spilled half of a large water bottle on one device (totally fine after taking the case off and letting the device sit in rice overnight to absorb any excess water) and dropped the other device all the time.
One of my biggest concerns with the Z3C was that Otterbox doesn't make a case for it. I eventually got a tempered glass screen protector (PThink) for the front and settled on an Incipio case.
I have now owned the Z3C for a little under 3 months, have dropped it frequently, had no issues..until last night. I dropped it less than a foot off the ground onto a wood floor, which is less than I've dropped it before. It must have hit just wrong, because now there are two large cracks running across the screen or screen protector. The screen protector's surface is smooth.
I also have small hands, and there really isn't much choice out there. So at minimum, if you get this phone, you must get a screen protector for the front. I never used them before, because the Otterboxes come with their own cover, but they are vital for this phone. I've ordered a new one and will wait to peel off my current protector to see what the damage is until it arrives...because if it's somehow fine underneath, I WILL end up dropping it again!