I think it's a matter of personal preferences. If you'd like a more quiet location, the YC is for you. It's the calmest of the 3 resorts, yet all the action is just across the lake at the Boardwalk. Plus the above posted good point about the availability of dining options inside the resort.
The BC, although just next door, is similar to the YC in every way, except it's much more noisy and active than the YC. Also the BC is undergoing renovations right now. I'm not sure when they'll be done.
The Boardwalk is my favorite, due to the activity. If you have a room with a view of Crescent Lake, the activity is right under your feet. In the evening you can sit out on the balcony with a bottle of Champagne and watch the world go by. The rooms are very nice, and you can quickly be out of your room and on the Boardwalk. There are also more dining options (ESPN, Flying Fish, Spoodles, Bakery, Brew Pub), but you do need to go out on the Boardwalk to reach them (that's my favorite part).
All 3 have equally easy access to EPCOT and MGM.
I agree with the other posters, you can't go wrong. Enjoy yourselves.