I prefer YC, but the two resorts are very similar. There is the issue of the balconies and that the YC seems more formal than the BC, as previous posters have mentioned.
BC is somewhat closer to the IG entrance to Epcot, but YC is closer to the boat dock for the boat to MGM (in both cases, however, it is a matter of a couple hundred yards, at most). The two resorts share buses, but usually pick up at YC first, which can mean that (during busy times) buses will fill up at YC, making it harder for BC guests to get a seat on the bus. The amenities and restaurants at each resort are easily accessible from the other resort, so that is not a big issue.
In the end, you can't really go wrong with either resort.