Have owned every iPhone since the 3G and have always gone naked. Apple's designs are just too good looking, and I am very careful with my phones. All that changed when I got the 6+, which was a little too big to hold comfortably. I started keeping a case on it because I found myself nearly dropping it quite frequently. Now that I'm back on the regular size for the 7, I'm going naked again. This phone is much easier to hang on to, and I haven't been able to find a case that doesn't completely ruin the wonderful feeling of sliding from the edge of the curved glass on the 6/7 series.
I did get a Rhinoshield crashguard bumper, but only use it at the gym or hiking, or anywhere else where a drop might be more likely. It's naked the rest of the time though. The matte black looks so sharp!