Epcot for me. No contest. To me it's like a two-for-one park with Future World and the World Showcase. So much to eat...er, I mean SEE, there, and the rides are cool too. I'm quite fond of Epcot.
Though I have to admit that my top choice for "last day park" is Magic Kingdom. I actually prefer Epcot, but it just seems like MK is the sentimental place to say bye bye to the Mouse.