If you only have 1 day, I'd recommend Epcot. You'll still have to pick and choose as you can easily spend all day in the different "countries" and still not make the other sections (nutrition, technology...stuff like that). All are fun.
I personally don't care for the Magic Kingdom much. Would be more fun, I suppose, if you have kids.
Silly is you in a natural state, and serious is something you have to do until you can get silly again.
Choose your friends by their character and your socks by their color...choosing your socks by their character makes no sense and choosing your friends by their color is unthinkable. anon