You are going during the holidays, so let’s start w/ decorations, the Poly has a decorated tree and other decorations best described as underwhelming. The GF has a multistory Christmas tree and a life size gingerbread house in the lobby and the grounds are decorated in what I’d call an understated elegance. GF in Dec. is far better.
What about the lobbies? Poly’s lobby feels cramped and crowded, crowds mill around waiting for the Luau show, Ohana, etc. & there is no entertainment. The GF’s restaurants are set back from the lobby with separate waiting areas thus the GF lobby doesn’t suffer from the chaos which is the Poly lobby. Certainly there are visitors @ the GF to admire the holiday decor & gingerbread house, but you can generally find a seat in the lobby to listen to the grand piano player or the band on the balcony upstairs.
Want to sit on your balcony and enjoy a drink and catch up chat w/ your friend? @ the GF you’ll have a balcony, at the Poly, maybe you will or maybe you’ll get one of those rooms w/out one.
The Poly has a more in your face frenetic atmosphere - which is fun, the GF has a quieter elegance that sort of creeps up on you and suddenly you think - ah, this is nice, really nice.
The TTC is walkable from the Poly, if you want to go to Epcot from the GF you’ll have to take the monorail to the TTC to transfer to the Epcot monorail.
I personally far prefer the GF, plus it’s pretty simple to monorail, walk or boat between the resorts.