I think Epcot. I really love lots of things in each park, and I definitely enjoy Epcot but if I'm thinking back on my last couple of trips, I think the least time was spent there. Next time I'd like to get back to taking a little more time to get through World Showcase. Test Track and Soarin' aren't big favorites of mine but I always make a point to ride Spaceship Earth and Living with the Land (the latter being my very earliest Disney ride memory, and The Land pavilion in general), and checking out The Living Seas,although I liked it better as Sea Base...
Most people pick DHS -- I'm not a big fan of the food there but I have always love, love, loved the "Old Hollywood" theme -- I spent a lot of time at my grandmother's house growing up, my parents love old movies, music etc. so a lot of that just had a "familiar" feeling to it-- especially last Christmas when I was looking at the silver tinsel decorations with the 40's/50's style reindeer decorations.... my grandmother died in 2015 so my nostalgia for that has only amplified since then I guess, despite DHS's condition the last couple of years. Not to mention RnR was the very first real rollercoaster I ever rode after my then-boyfriend-now-husband convinced me, and I love ToT -- again a combo of thrill and nostalgia as my dad watched Twilight Zone a lot when I was a kid. I do really miss The Backstage Tour though. It's fun how many different factors cause people to enjoy so many different aspects of the parks.