I have a matte black 7 and a jet black 7+, which I just bought to use as an iPad mini mini.
To my surprise I didn't love the jet black as much as I thought. Visually, I think I prefer the matte black. But the jet black feels great in your hand: silky smooth.
The 7+ feels very delicate, especially in jet black. It's like a heavy piece of black glass and I'm nervous about dropping it: I feel it would smash itself under its own weight. The matte regular 7 feels much more robust -- it's lighter and the back seems like it would offer better protection.
I don't actually know how the jet black is made (I guess there's an Ive-narrated video somewhere). Is it made of the same stuff as the matte black, but then with some amazing Apple coating?