III, IV, DX, and Bloodlines have the best combination of areas...particularly IV, which has so many mind-blowing areas.
BUT, if I have to pick one, I'll say Dracula X SNES' Atlantis Stage. It is absolutely gorgeous-looking, has great progression from low to high, and has a fitting selection of enemies for that environment. Plus, Annette is hidden there, it has some fun platforming with a flooding building, and its superior remix of "Picture of a Ghost Ship" works so much better with this stage than Rondo's pirate ship. Not to mention, getting to this hidden stage takes some skill as you have to maintain a key in the previous stage.