I don't own at either but personally if I were planning to regularly to go during that time, I'd probably pick BLT. Reality is you're going to need 11 month window for both if you want a chance.
Why BLT? With BLT when you book a TPV, you're guaranteed to get a true theme park view, Magic Kingdom is right next door. Poly has much higher
point charts and the view can be hit or miss. You can also walk back from MK to BLT much easier than you can walk from MK to Poly. When the most wonderful time of the year is also the most crowded, that's worth a LOT and is my personal pick.