Hi Joseline!
According to the
Disney Parks Calendar, the Magic Kingdom is the only Park offering Extra Magic Hours on May 13th. In fact, it is open until 1:00 a.m.! EPCOT closes at its regular time, 9:00 p.m. These times are subject to change, so make sure you check for any changes upon arrival.
So, if you are hoping to pack in the most that you can on that day, and would enjoy staying out late, then go for the Magic Kingdom!
If not, then I do believe that EPCOT is a great choice. If you don't plan to stay out until 1:00 a.m., then going to Magic Kingdom would not be the best because it will be a bit more crowded, due to the fact that it is an Extra Magic Hours day there.
Another great choice would be Hollywood Studios, which will be open until 9:00 p.m. also. The good thing here is that it is not as large as EPCOT, and you may be able to get more accomplished in a shorter amount of time, depending upon crowd levels.
I hope this is helpful! If you have any more questions, please don't hesitate to ask! Have a wonderful vacation!