That's a difficult descision. We are doing a split on our next trip. We have stayed at BC 2 times and Poly 3.
POLY
pros
Bigger rooms
Better transportation options
Wishes from the Beach.
The view from the pool without a doubt the best on property.
The monorail.
Best pool for young kids. Zero entry, easy to see the whole pool, beach to play on, splash area, great activites.
I love the longhouse set up. No long confusing hallways. Everything is close by.
Lots of dining options on monrail. Walkway to GF
Cons
No hottub
No Gym
BEACH ClUB.
Location. Walking distance to DHS and epcot.
Bright airy rooms
The pools is the best for kids over 8
Lots of dining options.
gym next to pool
Cons
Lack of CS.
Long confusing hallways
smaller rooms, tiny tiny bathrooms.
hard to keep an eye on kids at pool.
I really like them both, but if I had to pick it would be Poly.
Good luck