We have been fortunate to stay at both resorts, and they are indeed both amazing. I always think if you like Adventureland in the Magic Kingdom, you'll most likely enjoy the Polynesian. If you like Fantasyland, the Grand Floridian is a good match. However, we like them both!
For us, our next reservation is at the Polynesian, which does have a loyal following by many guests. We've grown to like the more relaxed feeling about it and the incredibly easy access to transportation: boat/monorail to MK; after a short walk to the Ticket & Transportation Center, we grab the monorail to Epcot; bus to the other parks. The Grand Floridian has a lot of people traffic and golf carts always zooming about that did bother us.
The Polynesian also has a nicely themed volcano pool with music even playing underwater, but there isn't a jacuzzi. I should also share that not all of the rooms have balconies, and some of the buildings have bathrooms where the sink is not separate.
And finally, the rooms at the Polynesians have been updated and quite lovely with their Seven Seas theming. The resort & rooms can be explored if you click
here.
I hope this helps. Please don't hesitate to ask any further questions if you have any.