I stayed at both back to back on a split stay last December and have about the same views as mickeynut1 (overall, I prefer Poly, but each has its advantages).
Poly advantages:
-I prefer the theming at the Poly and find that the resort has a more relaxing and enveloping feel.
-Rooms are bigger.
-Being able to Monorail to MK and EP beats being able to walk to EP and HS (not because riding the Monorail beats walking, especialy given how frequently the Monorail is out of service

, but because we spend a lot more time at MK than HS).
-I too prefer the Nanea Pool over SAB (it's more compact and the water slide, IMO, is better and much easier to access)
-I like the GCH lobby smell

better than the BC lobby smell.
-Wishes on the beach.
BC advantages:
-Very nice to be less than a 10 minute walk to World Showcase.
-Boardwalk area is within walking distance and is very fun and lively in the evenings.
-Bathrooms have a better layout (vanity separate from shower and toilet).
-SAB has hot tubs.
-Don't have to go outside to get from room to lobby area.
-Easy walk to your room after Illuminations.
-Less expensive.
FWIW, a splt stay at both of these resorts worked out GREAT for us (realizing that split stays aren't for everyone).