Lindsey, we were at the GF last year just after Christmas, but they were still celebrating the holiday season. You're right, the decorations are fantastic and the gingerbread house is a sight to see. I took a walk over to the Polynesian and IMO, it was very difficult to get the Christmas atsmophere in a tropical resort. For some reason, I always think of the Brady Bunch in Hawaii when I see the Poly. I know it's a favorite of many, my personal preference is the victorian theme, especially during the holidays. The only outer building that I've stayed in was Conch Key. It's probably the furthest from the main building & pool area, but that also made it very quiet. Another big difference that I noticed between the 2 resorts was the main building themselves. I didn't feel like the Poly's lobby was a spot where you could sit and unwind. At the GF, it's so big and open and at night you have the orchestra playing holiday songs in addition to Disney favorites. At any time you could find people relaxing on the sofa's and looking up at the beautiful tree.
I can't say if you'd enjoy one more than the other, they both have qualities that appeal to different people. The worst thing would be to sit on the balcony of one resort and look over at the other wishing you had stayed there instead.