YC rooms have full balconies, only about 50% of BC rooms do.
YC lobby is nautical, more understated, kind of makes me think of a library. BC lobby is breezy, beachy, casual.
YC is closer to the boat dock, Swan/Dolphin, and DHS. BC is closer to Epcot and BWI.
YC has the convention center so there are more business people around. BC is pretty much all families.
Their shared Kids Club is located in the BC.
To me, though, the biggest difference is the activity/energy level. YC is MUCH quieter and more subdued. BC is VERY hectic and lively. We had read that and decided to stay at YC as a result (we like a more relaxing feel to our resort stays) and were very happy with our decision. If your family likes a more high-energy resort, definitely go BC.