I prefer Bvlgari Black, by a wide margin. I own Black and have a large sample of Midnight In Paris.
Yes, they have a bit of similarity, but they definitely do not smell the same. MiP smells like a halfway point between BB and Armani Code, with a nod toward the feminine rather than the masculine, though it's absolutely unisex. That's ironic since Bvlgari Black is the one listed as unisex, not MiP, but Black smells far more masculine to me than MiP. To me, Black smells more mischievous. It smells darker and perhaps naughtier. It's more of an evening scent. I love it.
Both BB and MiP are excellent, and both are surprisingly affordable, but I choose (and love) Black. I wouldn't be surprised if many love them both, and I can completely understand why some will prefer MiP. As I said, they're both excellent, and they're both underpriced in my opinion. Without a doubt, they are different enough to be worth owning both.