I tried....I really did...but I can't pick just one. It's not possible.
MK - Haunted Mansion, Pirates, Splash, Peter Pan, COP
DHS - RRC, TOT
EPCOT - SSE, (Horizons

) LWTL (sweet little ride that really appeals to me for some reason)
AK - (haven't been on EE yet...can't wait for that and I have no doubt I'll love it) but w/o going on EE, Dinosaur. I love the AK park itself. Just walking there and soaking in the atmosphere and beauty of the park.
For me, it's all about stirring my imagination through the theming and attention to detail. When budget constraints result in corners cut in the details, it takes a serious toll on the guest experience. (cough.. JII...cough). To be totally immersed is what takes it from a ride to an "experience" and that's what sets Disney apart.
The best moment for me on every trip is that moment at MK when the lights go out and the fanfare for
SpectroMagic begins. I get a lump in my throat and a feeling I can't describe comes over me. Silly, I know, but I love that parade and I anticipate that one moment of every trip. I really love all the shows. Spectro, Fantasmic and Illuminations are all "must do's" every time.