OK, I'll be the dissenting opinion. We love the WL.
Actually, the answer to the question depends on when you are going. If it is after Thanksgiving the WL wins hands down. Once the Christmas decorations are up the WL is incredible. It is wonderful any other time, but it is best during the Christmas season. WL does have boat access to the MK which is convenient. The quiet pool at the WL is soooo relaxing, including a big hot tub. There are more activities at the WL, the guyser is neat, and the lobby is incredible. So many comfortable places to sit and relax. Relaxation is what the WL is all about.
The BC is a great choices as well. While WL is tops for relaxation, BC is tops for non stop action, it is a very bustling resort. The location is tops, and with older kids it may be a big plus for you if they like Epcot and MGM more than the MK. You can walk to both Epcot and MGM, or take a boat. If you plan to spend more time at these parks than at the MK the BC is the better choice. The pool at the BC is the best on property. There are lots and lots of restaurants at the Epcot resorts, and the BW is right there. The rooms are a little larger at the BC.
Very tough choice. To be honest with you, we are going to try to stay at both on our trip the week after Thanksgiving - 5 nights at the VWL and 3 at the BCV. We split our stay between the CSR and WL last year and it was neat to see two different places. How many nights are you going? Just an idea.
Good luck deciding.