You want to be in the French Concession area. The Shangri-La is there as well, as is the Puli. Both are good. You do not want to stay in Pudong or Hongqiao. The Expo side is Pudong. It's too far removed from the good stuff.
There is only one exception I am willing to make and that's the Peace Hotel on the Bund. It's just a classy place worth it for the experience.