Here is a list of tours I have taken for Epcot. Just a word of warning for the oldest, some tour there are not too many people, others you can be split into groups of about 12-15 people if it is a popular tour.
Future World: History of bringing Epcot to life, facts and ride on Spaceship Earth, Fountain of Nations history, significance of moon outside of Mission Space, view of aquarium at Coral Reef before opening for lunch, history of the Land building, since there was just 4 people total on our tour we got a bonus look at how they wash all the 3D glasses from all over WDW, history of Imagination building and Figment, information on monorail, Wonders of Life building and Odyssey building, visit to one of the 3 VIP lounges, backstage and ride on Test Track then finishing the tour backstage at Cast Members Services.
Destinations: Picks up where Future World left off with Fountains of Nations history, stop and history of each country of World Showcase (I never realized how much artwork is on display for each country), history of and backstage view of Illuminations barges and globe, and lunch at Rose and Crown.
Behind the Seeds tour is short and for all ages. You become part of the Living with the Land ride as you learn about aqua and hydroponic gardening, the variety of plants within the area and how everything in the ride is used by Epcot restaurants.
The Royal Tea Tour was another short but very informative tour of the tea cup planters in the garden during Flower/Garden Festival, a history of the Twinnings Tea Company and ends with tea and scones at Rose and Crown.
I can recommend the Marceline to Magic Kingdom tour as a shorter tour. You will get a history of Main St that reflects Walt's life growing up that starts at the train station progresses down Main St. The best part of the tour is stories in the Haunted Mansion que, a ride on and then going under the ride to see how it functions while the ride operates. We took a break at Tangled area and finished the tour with the history and ride on Carousel of Progress.
The Keys to the Kingdom is also a good tour relating a history of
Disneyland which inspired WDW with rides on Jungle Cruise and Haunted Mansion. We went backstage to the parade barns, trash collection area, and ending with the utilidors,