For my family, park day planning revolves almost completely on avoiding morning EMH. If we're only going to MK once (rarely happens), I plan it for later in the trip because I'd rather have the build up to my favorite park and end the trip on a high note. But I can recall my first trip to wdw as a kid. I couldn't wait for that quintessential view of the castle I'd seen a million times in commercials. For that reason I was disappointed that our first day was spent at Epcot. I was a scholarly, bookish child who loved the idea of travelling the world. Given my personality, I would have still loved Epcot even if we had gone to MK first.
Funny enough though, my favorite park as a kid was the studios. It was such a cool experience once upon a time. Somewhere over the years it lost it's focus. Now, with the park almost gutted, I am more than happy to skip it. Which leads me to the suggestion of spending a half day at the studios (if you plan on going) and heading back over to the MK so you get two days of MK.
