Having stayed at both with kids, I would say Poly if price is no object.
I love the WL and think that over-all the theme is more impressive and perfect for winter travel - nice warm cozy feel inside with no walking outside to get to other parts of the resort.
Poly wins hands down for transportation with little ones - the boat and the monorail are fantastic. You could spend an hour just riding them around on the monorail and they'd be thrilled. It was a great late night thing I could do with DS before bed - ride the loop past the MK, switch at TTC for EPCOT, switch again and be back at the resort. It was some of our most magical time.