I was never impressed with the original Orgrimmar. Just some ragged huts in a canyon, it never felt like a powerful capital to me the same way Stormwind did. Now though... man. Orgrimmar is amazing. A mighty fortress. Immediately you know the power of the Horde when you're in Orgrimmar.
Stormwind is also very nice. It feels even more "lived in". In some ways it feels more like an actual city than any other capital in the game.