Several things to consider here.
I would say, ask yourself do we want rides or relaxtion. If I only had one day to spend at WDW with my wife, I would most certainly go to Epcot. Although I love riding rides, I would rather spend a good day at a park with fewer "thrill" rides and take in the "after hours" setting that is created at Epcot World showcase.
As a matter of fact, on our upcoming trip to WDW in December, I have already explained to the kids (17, 13, 9) that Mom and Dad will be taking an entire day at Epcot by ourselfs and that we will see them back at the hotel. Normaly we wouldn't do this, but our children have been to WDW many times and we all have cell phones. Our oldest is a very responsible young lady and the other two are well behaved and know what is expected of them when they are out in public.
Good luck and have fun on your day.