I would rather get the matte black for the obvious reasons but jet black is a mixture of looking tacky and sexier in photos. Yes, iPhone 3G/3Gs-like or a black iPhone 5c. The Darth Vader iPhone 7. Matte black doesn't even look true black and for most showoffs, nobody could tell if you had a 6/6s or 7 since it is just a darker space gray.
I personally don't like dual tone phones. Whatever I see on the back should match the color on the front. Still, I would get matte black if I had to choose. But I wouldn't close the door on jet black considering I want black onyx Note7 which is glass and invites scratches and fingerprints in any color. The jet black reminded me of the Xiaomi Mi 5. The render of the "space black" looks closer to the jet black than the matte black.
I want to see a durability test on both black and jet black. Most people really can't make a final decision until they finally see it in person. Matte black also invites fingerprints like any black color and I want to see if it scratches, different color like what happened to the slate iPhone 5 and HTC One M7? The jet black is aluminum but the glossy plastic layer might be similar to 3G/3Gs where if it scratched up, same color underneath although it might depend if the scratches were shallow and not so deep.
The way I see it is like comparing original PS4 vs PS4 slim and Pro or og PS3 vs its slim revisions. The newer ones went matte black and lost its bling and pizzazz. The older one looked hotter but the glossy finish attracted fingerprints. Rather get black iPhone 7 since I am practical but jet black really did surprise me andI did consider getting a 256gb jet black. The showoff in me sometimes wants others to know I wasn't holding just a 32gb iPhone 7 and darker space gray. For four hours after the announcement, jet black was really on my mind even though matte seems more practical to own. Can't underestimate the power of the dark side!
Just wait for the durability tests. Our fingerprints also has more tractions if jet black. I want to see how well the jet black holds up to scratches. I just find it strange that $800+ Note7 and jet black iPhone 7 can invite scratches and fingerprints so easily while phones under $100 can maintain looking cleaner. The matte black iPhone 7 might show less fingerprints BUT if scratched up, you are going to have to live with that silver color underneath forever. You asked for metal. Plastic and glass aren't that way.
^ The One M7 on the right was a fingerprint magnet too and is matte black. Glad I went with glacial silver which maintained its clean-look. Just remember, either glossy and matte in black will attract fingerprints. The scratches underneath is my deciding factor between the two.