If I am going to a Disney World park by myself, lately I seem to gravitate toward Animal Kingdom and that surprises me.
Animal Kingdom is far more than some fancy zoo. I tend not to ride the attractions as much but I will find myself considering Avatar: Flight of Passage or hitting Kilimanjaro Safari just about every time.
I tend to spend more time around the Africa section and a lot more time taking the Gorilla Trek and the Asian walk to see the Tigers. I will sit through the Nemo live action show and simply just enjoy the atmosphere maybe more than any of the other parks.
A.K. relaxes me. There is nothing glaring that you feel you need to do or feel you are missing without friends and family with you.
Food options are easy to come by and drinks flow easy as well. While you can just take a seat at EPCOT and enjoy a beer or something else, Animal Kingdom also offers similar options with many of them coming with animals to watch while you chill.
It's a close one to be sure but if you are planning a solo adventure, you can't go wrong with A.K. any more than you can with EPCOT.