Most: The Magic Kingdom, especially (for me) Cinderella's Wishing Well. When I was 7 years old, I wandered from my parents one night and stumbled upon this simple fountain; this area feels so quaint, cozy, and comfortable that it whisks me back to classic Disney magic everytime I see it.
Least: I don't find that any one park completely lacks its own version of Disney magic--even AK relates to Walt Disney's True Life Adventure films. However, the dilapidated WoL pavilion, SGE, the NY street area of D-MGM, and Dino-Rama (especially Dino-Rama!) all lack Disney's definitive magic. Well, WoL once had it...
Worse (my new category): The arm/wand on top SSE is possibly the most contrived, fake "magic" at WDW. It's a meaningless, soul-less imitation of the true wonder and real-life "magic" that's celebrated at Epcot.