The title says it all. Which is your favorite Raid and Dungeon? Give a brief explanation of why! Maybe someone will give you a good reason to re-visit some worthwhile old content.
Favorite Raid - Karazhan - Because it's one of the only raids that feels to me like a real space that you can move around in and explore, instead of just a series of neat-looking but arbitrary big rooms with big bad guys. Loads of lore, excellent encounter design and diversity, and the most immersive raid zone, for my money's worth.
Favorite Dungeon - Ahn'Kahet - The Old Kingdom - Because it's the most visually striking zone in the game for me. There's such depth to the space inside here; so many intriguing things out beyond your reach that make the Nerubian underworld feel like such a huge and mysterious place that you're barely scraping the surface of.