Ultimately, this decision needs to be yours. The parks are completely different, aside from from the international atmospheres created in both and of course that Disney magic.
Have you been to the parks before? Both or even one? That would a big factor for me. I love to experience new things. Epcot is open later than DAK, because of the intense animal care required. DAK closes with the sunset--it's only natural.
Now, I never got to experience DAK as a guest. The first time I stepped foot inside DAK, I was training. I learned so many cool things about the park that I wouldn't have picked up on as quickly on my own. These things made it special. I learned how to visit this park the way it was intended to be visited. I get a lot out of it. If you choose DAK, take your time and really take in and respond, naturally, to your surroundings. It is not your typical theme park--it's not fast-paced: go, go, go!--And, it was never intended to be that kind of park.
Epcot is in one word fantastic. I love all of the parks, but found myself spending a lot of my free time here for the food, the people, and just the overall atmosphere.
Now, if you decide to buy a Park Hopper and race through DAK, which I don't recommend for your first visit, but it's very easily done. You can also experience quite a bit of Epcot in the same day--especially if you're staying on property and get an EMH day. Again, I don't recommend racing through the highlights, but it is an option. I've done this on a few occasions. Good luck with your decision!