My parents and I always try to score any of the rocking chairs in the Magic Kingdom. Once we watched the new Fantasy parade from the rocking chairs of Town Square Theater. Awesome viewing. I highly recommend it.
Probably the best area for me is toss up in Animal Kingdom. I could probably sit anywhere and be happy. The water seating area at Flame Tree Barbecue gets top marks though. I love sitting there watching the trains go up Everest and see the clothes the washer women left on the steps although I don't know what the view will be like now that Rivers of Light is being installed. I hope they don't take away some of those details.
But if they do, I will always have the trails by the Tree of Life. They are absolutely gorgeous! If you've never experience it, I urge you to go there, sit and listen. The softness of the background music and how close you get to the tree is enchanting. You feel like you are the only one there with the Tree towering over you. I wish I had the words to accurately describe it. Plus there's a hidden hole in one alcove where you have peer through and get a good look at the ant that carry the seed for the Tree of Life to where it is today. Absolutely the best.
At the Studios, it use to be the Backlot Express directly across from the Star Wars stage. After I would spend my days off at Animal Kingdom, I would close the night with a couple of viewings of the Jedi Training Academy before going to see Fantasmic. I loved the old show because it was funny, and I enjoyed seeing the kids try to wield their lightsabers. I could sit under the umbrellas and go get a refillable soda just a few feet away. Now that the show has lost the funny moments, I don't think I'll be using that spot as much as I did.
I'm a little ashamed to say that I don't have a favorite in Epcot, it's usually too windy for me to sit outside anywhere near the lake, and I don't care much for sitting inside because I like to people watch. The quest is on!