I've got to go with 2008, I thought coming up with that entire back story on Bloody Mary and the way they played it out on the site last year was great. The flying monkeys in the park were incredible, and I've always enjoyed the Scary Tales themed houses.
Even though I didn't go in 2007, I thought that year's website was the best out of the options above. If I remember correctly, didn't that year's website have interactive puzzles to solve before revealing additional material.
In my opinion, the best year for the HHN website was 2005 with the Terra Queen.