We have stayed in the BWI deluxe room and at the WL, but not in the deluxe room. Generally, I recommend the WL fir Christmas or the GF. In the Epcot area, I would recommend the BWI at Christmastime. Two reasons that I might choose the BWI over the WL would be 'That deluxe room is amazing!' And the BWI CL is a favorite. Also, the BWI rooms are typically more than WL rooms, are they not? So, if the price is the same then it is a chance to see the BW for a comparable price. Then again, if you are staying in the GF soon, you will be staying in the MK area then, so I would stay in the Epcot area to change it up. Although we prefer to stay in the MK area resorts, we do like to stay in the Epcot area on occasion. In addition, you say that you have stayed in the WL before but the BWI is new. We like to experience all the WDW resorts in a kind of rotation, so we would choose BWI for that reason also. Finally, I never knowingly book a resort under construction and the WL should be under construction during your visit. (OK , that's more than two reasons!)
Bottom line:
Despite the fact that the WL is usually neck and neck with the GF for a Christmas resort in WDW, I would suggest the BWI this time for your group.
Good luck choosing!