My vote would have been for the Magic Kingdom, but the poll is closed.
I like that EPCOT exists. I am glad it is there, with its big golf ball icon and its fine restaurants. I enjoy Mission:Space and am looking forward to seeing Soarin' when it opens. I like walking around the lake and spending a little time in the various pavilions of the different countries.
My problem with EPCOT Center is that the major pavilions have not stood up well to the test of time. I haven't had any desire to visit Energy or the attractions inside The Land in years (I will eat at the Land's exceptionally nice food court!). The newest version of Imagination hasn't received very high marks on this board. My kids were unimpressed with SpaceShip Earth, the last remaining pavilion with updated AA figures since Horizons, Motion and the original Journey Into Your Imagination have been sent to the scrap heap. Test Track is always broken when I visit. The last visit to The Living Seas was disappointing as compared to past visits (the absence of cab boats makes that much difference, I guess), and the fact the entire pavilion devoted to the human body has been closed for so long (is it open for summer?) says to me that Future World is at a crossroads and its future is uncertain.
On the other hand, the Magic Kingdom not only endures, but prevails. Old classics continue to connect with today's children (unlike SSE) and the mountains scratch the thrill itch. Newer attractions like Buzz Lightyear and Philharmagic have been a big hit. The Magic Kingdom takes you to a fantasy world, while EPCOT takes you to a corporate world, sponsored by Hewlett Packard or General Motors or AT&T or the other highest bidder. When the Magic Kingdom does get a new "E-ticket" ride, watch out!
It isn't a close vote at all for me. If I am going to take a one day trip to Walt Disney World and have to choose between these two, I'll be on my way to the Magic Kingdom.