For that date range, I would keep Poly (at least for the first part of the stay) for the MK Halloween fireworks viewing. Given the length of your stay, you could do a split stay and stay the first few nights at Poly and catch the MK Halloween fireworks from the resort (if you aren't going to the party) and then do the last part of your stay at BWI. We do this type of split stay a lot and it works out really well for us (though we don't have kids, so the move day is easy for us).