I could make a case to myself for DHS, AK, or maybe even Epcot as my least favorite.
Epcot: Such a poor, pale shadow of EPCOT Center, which actually would be my favorite of the four if it still existed. Future World is probably the most depressing place in WDW to me. I still visit for World Showcase, though.
DHS: Really struggling to find itself. Too many shows (that have been running too long) and not enough rides. Closed attractions. However, the park has one of my top attractions in Tower of Terror, and I also enjoy RnRC, even though it's too short. And Star Tours 2.0 is a huge improvement.
Which leaves AK. Absolutely beautiful park (especially Asia) but experience-wise, surprisingly empty. KRR may be the worst attraction in WDW (worse than Stitch, I think). Broken Yeti. Hot, humid. I'm a local AP holder, and I never go. So I guess AK would be my answer.