Best experience?
Best Rides?
Best Park?
Best Meal?
Overall best or most surprising thing?
Having just gotten back from my first-not-really-first WDW solo trip (I did the College Program a decade ago, so I spent a lot of time solo on my free days but didn't have money for upcharges, wasn't
really there purely as a guest, etc.):
Best experience: Wild Africa Trek. I did a bunch of upcharge stuff on this trip and it was a mixed bag as to how much value I felt I got out of each, but hands down, zero question, Wild Africa Trek was worth it. The guides were a ton of fun, I learned new things about the animals and about AK's brand of zookeeping even though I already had at least some familiarity with all of it, and the lunch they served was delicious.
Best rides: In a broad sense, the best thing about rides as a solo traveler was doing things as many or as few times as I wanted. I didn't ride everything, but the rides I skipped were ones I didn't really miss. I didn't feel pressure to do headliners on repeat just because they're headliners. Conversely, at Animal Kingdom After Hours, I rode Dinosaur seven times in a row without even exiting the vehicle, and I rode N'avi River Journey six times (they make you get out and walk a whopping twenty feet to get back in the boat on that one), because I wanted to and there was no reason I couldn't or shouldn't.
Best park: This time around I'd say it was DHS. I spent a lot of time there, and snuck in a few extra hours here and there, mainly because of Galaxy's Edge. Exploring SWGE alone was pretty rewarding--I could spend however long I wanted playing around on the datapad while sipping a blue milk, I could navigate crowds to watch character interactions (and got a talking-to from Vi Moradi about focusing my efforts on helping the Resistance when she caught me messing with a crate using my datapad), and I didn't feel any pressure to move on to the next thing or worry about getting on more rides when all I really wanted to do was enjoy the atmosphere. Epcot comes in second; I did Figment's Brush with the Masters scavenger hunt and spent half a day literally just wandering the World Showcase pavilions looking for paintings and checking out the shops. That never would have flown when I was traveling with family.
Best meal: Skipper's Canteen! Delicious food, funny server, overall a really good time. Honestly I had very few bad meals, and I was glad that I took time to do more table service meals and lounges. That's something I think I can carry over into my next shared trip, though, since my housemate also enjoys good food and downtime amidst the hustle and bustle.
Overall best: de-optimization. I had a schedule planned out for this trip and I surprised myself by mostly sticking to it, but I think it worked out as well as it did because my plans were relatively broad, consisting mostly of which park to start at and deadlines to leave places in order to make it to various reservations. But the thing that was surprising and refreshing to me was that for the most part, I didn't ride things more than once or twice, and I didn't consider that a failure. I didn't have my phone or camera out to record things during attractions; I was just present and engaged with what I was doing and I let each experience be special--quality instead of quantity. I think because of my CP background and because of the prevailing attitudes on these boards I had gotten swept up for years in the idea that if I didn't ride my favorite rides literally as many times as possible while maximizing FP+ use and using every trick in the book, I was somehow failing at Disney. I just threw all of that away and enjoyed things as they came and let myself take time to do what I actually wanted to do--and if something I'd planned no longer sounded like fun, I tossed it and did something else. For instance, I'd planned to see the parade at MK before leaving for dinner at Epcot, but about an hour before the parade I realized I was kind of tired and cranky and that staking out a spot didn't sound like fun. So I left and chilled out at the Polynesian until Trader Sam's opened, had a couple of drinks and a
fantastically fun time, and then went on to Epcot from there. Zero regrets.