As you can see, everyone has varying opinions. It's all about personal preference. Check out allears.net or the Disney website and look at all of the attractions each park has to offer. Go with the park that will be the best fit for your family.
Epcot has : Test Track, Soarin, Turtle Talk, Spaceship Earth, Mission Space, Honey I Shrunk the Audience, Imagination, Innoventions, Ellen's Energy Adventure, Living with the Land, Charater Connection, Illuminations and The World Showcase.
MGM: Star Tours, Indiana Jones Stunt Show, Voyage of the Little Mermaid, Playhouse Disney Live, Beauty and The Beast Live, The Great Movie Ride, Lights Motor Action Stunt Show, Honey I Shrunk the Kids Playset, Rock n Roller Coaster, Tower of Terror, Stars in Motorcars Parade, Muppetvision 3-D, Backlot Tour, Animation Couryard, and Fantasmic.
As far as characters go, both parks have opportunity for character interaction, at Epcot there is the Character Connection and other characters in World Showcase. At MGM there are characters at Animation Courtyard, New York Street, and Al's Toy Barn. Also at MGM is the Stars in Motorcars parade Fantasmic, and the live shows where characters can be seen but not approched. No matter what park you chose make sure to check the times on the "Times" schedule to see when and where the characters will be.
Chances are that the kids will prefer 2 days in MK rather than visit a different park. IMHO
Good Luck and Happy touring.
