Here is my opinion after staying at both more than once. I love the AKL but in my mind does not beat the Polynesian.
For starters the rooms are not slightly bigger at the Polynesian but much bigger. I did measurements of the rooms (for a guide book) and this is how it comes out.
The square footage of the AKL standard size savannah view room I was in measures out to be 339 sq-ft
The original longhouse rooms are 415 sq-ft
The newer construction in 1978 and 1985 rooms are 476 sq-ft (which are about 42% of the rooms on property)
The Polynesian rooms are being completely redesigned and should be done way before Christmas. Both do about the same level of decorating but the Polynesian even changes the music around the resort to Hawaiian Christmas music. You can watch Wishes every night from the beach and you can easily visit the GF to see what is probably the best Christmas Decorations on property. You will save quite a bit of time with the Polynesian transportation. If it is raining you can visit the GF and Contemporary to shop or eat with out ever going out in the rain.
You said you were doing Garden View, not concierge right? Well Hawaii longhouse is concierge only and yes the rooms have been done in Hawaii and look like the other renovated rooms.
We are going in December but if you want concierge you might have to do Lagoon view since the garden view concierge rooms were booked for our dates and even most of the suites are gone. In fact they said there seems to be a mad rush on reservations for December already.
I have a few photos of the Polynesian at Christmas on this page
http://www.tikiman2001.homestead.com/poly12.html
Aloha
Steve