Trying not to be biased, but Hong Kong here as well.
Pirates is amazing, the best thing Disney have done, and Tron is my favourite Disney coaster, but that's kind of all there is. Most Disney parks are way more than the sum of their parts, but Shanghai really isn't. It is all quite soulless.
Hong Kong is definitely the most chilled of all the "Magic Kingdom" parks. You don't feel like you're rushing around trying to get everything done. Like Sue said, you've got the train and station which really sets the whole thing up before you get anywhere near the actual park. The shows, other than the castle/fireworks - which no doubt will undergo massive improvements in a couple of years - crap all over the ones in Shanghai, too. And yeah, Halloween is stunning.