I really like the Jet Black iPhone as well. Have only had this one for a few days, but its a nice phone to look at. The smudges don't even annoy me and no scratches to the naked eye thus far...and I have handled it pretty rough. I think as long as you're not poking it with knives like these scratch tests, you will be fine lol
Its really slick looking, reminds me of sort of a black iPhone 3G/4 cross in a lot of ways but not entirely (due to the lack of the steel band)
I like how it hides the antenna lines, and my favourite thing about it is how much "gripper" it is than the other aluminum finishes
That said, the main downside is that doesn't feel as premium...I know it is aluminum, but it doesn't feel that way, at least not to me...it doesn't quite feel like glass either and not quite plastic, but little things like pressing the buttons do feel "plastic-like" which is a bit strange...it certainly looks premium but doesn't quite feel that way...it is hard to describe since it grips great but has a somewhat "toy" like feel. Its super weird to me, since - again - it looks fantastic.
Also, regarding the sentiments people had about the SIM tray not being flush with the phone: mine was initially not flush, but after I put my sim card in and put it back, it did become flush. It seems like you just need to push it in, and all is well. Mine is 100% flush, no different than on the 6s for example.
All in all, a great looking iPhone, and nice to grip in the hand....I also had a matte black one (and I may yet get that one again) and that one was pretty slick too...