My DS 4 loved Epcot. We spent two full days there in March. If you get the PH option, the best plan is probably to try it and see, then hop to MK if it does not work (unless that day happends to be an MK morning EMH, of course). It really depends on the child. My DS is very into computer and video games and loved Innoventions, as well as Spaceship Earth, Test Track, Living Seas. Loved watching the acrobats between world showcase and future world and playing in the fountains near there. Loved th eMexico and Norway boat rides. Loved eating in Norway (lunch -- now defunct, to make room for the Princesses) and Morocco (dinner -- belly dancing with audience participation!) and Mexico (very cool any time of day). Also the boat to play on in Norway. Meeting Pooh, et al in Britain. Making crafts at the kidcot stations. Sending emails to grandparents in Mexico.
But...if your DD is into Princesses, I can see how more time with Mom at MK might be best. I so wish I had a little girl so I could have an excuse to do all that stuff! LOL!