I love staying at both! The GF truly is "grand". The rooms are nice with indoor corridors in the different buildings. 2 nice large pools, and wonderful restaurants and shops. But, if you want to feel like you're in Hawaii, then Poly is great! The longhouses are nice and rooms are very well appointed, about the same size, maybe a bit smaller than GF rooms. Wilderness Lodge is my husband's favorite though. No monorail, but boat to MK is very nice!
GF is WDW's "flagship" resort, so you just can't go wrong in any way staying there IMHO. But, is it worth the $$$$$$. Not sure, unless it's a special occasion. The grounds at both resorts are lovely, but there's something romantic about the POLY, and I can't quite put mu finger on it.