>>44882588If you're ranking the games just as they are, without any outside interaction, than Black 2's Challenge Mode is better as it allows you to fight harder versions of the post game bosses for a greater challenge while White 2 just makes the post game easier. On their own without swapping things you can make an argument one way or another for whether the city or hollow or w/e is better, but having the ability to up the difficulty for yourself whenever you feel like it is objectively superior to lowering the difficulty of an already relatively easy game.
Also it's worth noting that the shiny Gible is actually the ONLY way you can get one in Gen 5 without transferring. Dratini can be found in the wild, but unless you own a Sinnoh game and another DS to transfer with you're not getting a Garchomp in Gen 5 without clearing Black Tower.
I get that they're technically the same game but it was my list of opinions and I feel like Black 2's version exclusive content significantly outweighs White 2's. So I put one above the other.
Also Kyurem Black is one of the gorilla arm dragons and is one of my favorite pokemon. I mostly put that reason there as a joke (it's entirely subjective, I know), but I do have a fondness for his frankenstein's monster design of a dragon. 
