If you’re going to put your iPhone in a case, then it doesn’t really matter whether you get regular black or jet black, because when encased, they’re nearly indistinguishable.
I’m frequently complimented on the bamboo case for my iPhone 5S (photo below, taken with my Macbook’s webcam, apologies for potato quality). It’s relatively distinctive and adds a non-negligible layer of protection.
I subscribe to the notion that phones should always have a case, because this is a friggin’ expensive piece of equipment that will be exposed to all sorts of abuse. And since I try to run on a 3-ish year hardware refresh cycle, the device needs to hold out for that long.
(It’s the same reason I have a hardshell for my Macbook Pro. It adds a layer of protection, and also gives me a guilt-free surface to place stickers on!)
Now I get that not everyone agrees with this philosophy. I see all those unprotected phones when I’m on the subway. And I get that the aesthetics of a naked phone matter greatly to some people.
But if you’re going to put your phone in a case, the colour doesn’t matter.