Are you kidding! Diamond has a lot better Pokémon than black does according to the Sinnoh region pokédex. The starters are really cool! When I first started to play diamond it was very fun. I currently beat the game in 38 hours and 58 seconds. It is the best region!
I played both of them soon after they came out and I have more memories with Black than I do with Diamond. In Black you can only use Unova pokemon to get through the game until you beat Ghetsis and then you can get pokemon from other regions. I thought that was a cool concept, but I can also see why other people didn't like it as much. I loved the music, the feel, and the story better than Diamond. That's just my personal preference.