Find your niche.
I don't think it's fair for the Black version of Opelucid City if I say I like the White better, because I've never really reached Opelucid when I played Black. But even though I never really saw it in-game, I still think the city is a little less appealing there when compared to what they did with it in White. I thought the concept of White's Opelucid City was unique and interesting, and that it wasn't just a generic bustling city. Plus the music is better there, and that's usually all I care about with towns and cities of Pokémon games (unless I really like its concept or atmosphere).
So yeah, I'm picking the White one.