Hi Amanda!
Both of those resorts are great! My personal favorite is the Boardwalk. I love that you can easily walk to Epcot and take a ferry to Hollywood Studios. The parking lot is convenient to the resort, and you have the entire
Boardwalk area to browse around in when you aren't at the parks.
If you plan to do afternoon naps, and then have dinner at Epcot, I think the Boardwalk would also be more convenient for that. You can enter Epcot through the back of the park (International Gateway Entrance) and be at the restaurants within 20 minutes of leaving your room.
Again, I think both resorts are great, but it sounds like the Boardwalk would be a better fit for your needs.
Please let me know if you have any other questions as you plan for your race. The Princess half is so much fun!