Definitely Magic Kingdom. The only caveat to that is if ROTR is a must-do for you, you might want to build in some flexibility to park hop as necessary - that way if your DHS day is a "bad" ROTR day, you'd have some flexibility to go back in the morning, maybe on your Epcot day for example. We were on a longer trip last week (9 park days), but split up Epcot and AK into multiple half-days. I think AK is nearly a full-day park with the addition of Pandora, but it was still nice to spend open to 3pm or so, then go back on another evening to experience Pandora at night.
A lot depends on where you're staying too. We were at Yacht Club, so hopping between Epcot and DHS was easy.