O.K. I've been to both, I'd pick the Poly here are my pro/cons
Poly
Pro: Relaxing feel. Pool located ith GREAT view of Cinderella's castle, nice slide and zero entry. Can watch EWP and fireworks from beach. Tiki torches at night. VERY large rooms. Casual atmosphere.
Con: Room decor, too dark IMO. Some rooms have musty smell. No balcony on 2nd floor of older longhouses.
GF
Pro: Beautiful resort. Pool is just as nice at Poly with one exception (will be in cons). Also can watch EWP and fireworks, but from dock, not beach. Nicer room decor IMO.
Con: Monorail passes just past pool, not relaxing IMO. Snotty CM's and managment. Too formal at times. Restaurants are wonderful, but pricey, even GF Cafe.
Now, this is assuming a non-concierge stay, if going concierge, RUN don't walk to the Poly!!