Animal Kingdom has the Safari, Dinosaur ride, a carnival themed area, Expedition Everest roller coaster, Kali River Rapids, the jungle trek. So if you think your kids would like all of that, and are interested in animals, I'd say chose that one. It also has Finding Nemo show and the very popular Festival of the lion king (closed right now).
Epcot has in terms of rides: Test Track, Sourin, finding Nemo ride, Spaceship Earth, Mission Space, Living with the Land, Gran Fiesta Tour (duck ride), Maelstrom. Im sure Im missing some rides but these are the main ones we go on. It has Club Cool (to try free sodas from other countries), and of course we love sampling the ethnic foods in World Showcase! Epcot also has a beautiful fireworks show at night over water, Illuminations.
We would always chose Epcot over AK just because we feel it has more to offer but of course that is just my opinion. My kids did love the animals at AK and we had a nice time but we feel Epcot holds a little more magic for us. we also have been when they do their flower and garden festival and the topiaries are so pretty!!
If you want your children's input, I would google YouTube videos of both parks and their rides and see what one interests them more.
Edited to add 1 more thing: HS is great for young kids that are into Star Wars for they have the Jedi Training Academy ( kids get up on stage to fight Darth Vader- So awesome!!) then there is Star Tours ride, Toy Story Mania, rock n roller coaster. The beauty and the beast live show, voyage of the little mermaid. Indiana stunt show, muppet 3d show. Fantasmic show at night. I am partial to that park because my son is an avid Star Wars fan!! Disney junior characters are there and so cute! I think they have the disney jr show too. It's a smaller park so not as much walking as the other parks.