YC seems a little more serene to me. Lots of conventioneers, but you only see them sporadically because they're gone at convention most of the day.
The BC side is more crowded and louder, more kids and families everywhere. Lots of people coming and going through the IG, plus the villas are on that end, sharing the BC amenities, so that all adds to the crowds.
If you're planning a trip, keep in mind that the BC rooms are undergoing refurbishment right now (should be complete in the fall) and YC will start its refurbishment then.