My five year old also loves Epcot, and has enjoyed it since his first visit at age 2. He likes all of the parks, but on our latest trip I think we spend more time at Epcot than any other park. We enjoyed snacks around world showcase and the agent p game, nemo and turtle talk, mission space, Ellen's energy adventure (may be too intense for the little one), test track and soarin, the land boat ride (he has always loved this), imagination (he loves this, too), spaceship earth - his favorite ride at Epcot, as well as enjoying minor attractions like the fountains and the light up squares on the ground near spaceship earth, and the entertainment around world showcase. Our son also enjoyed talking to some of the folks working at Epcot from other countries, and visiting the stores there.
Of disney parks, we put DHS last. Our son does enjoy star tours, but there is less in that park to hold his attention.
From the other responses it just seems like all kids are different in how they respond to the different parks. We assumed our son would like Epcot based on his interests, and he did.
We went to universal for the first time this year with our sons. The infant couldn't do much, but it was a great first trip to universal and IOA for the five year old. I posted a trip report on it. I agree that you may want to postpone universal so you can make the most of it and then avoid having to choose between disney parks. We loved our visit there, though, so I would highly recommend visiting sooner or later!
Good luck with your decision and enjoy your trip planning!