WE really like the CR garden wing rooms, especially on the ground floor. Would you be planning to go to Epcot often? The CR is great for the MK, but going to Epcot is the one destination where you have to use the monorail from the CR. Well, except if you walk to the MK bus stop and use the bus to BC and go in through the IG (which is what we often do going from CR as I am not a fan of the monorail). In the past I would have suggested a split stay but the new booking window issues for FP+ means you really have to stay in one resort (or so it looks for now).
WE have used the small elevator to go to/from the monorail platform at the CR and it can mean a few minutes wait on times. Getting to Epcot from the CR is its biggest transportation issue, IMO. The biggest positive, OTOH, is the walk (or
scooter ride) to the MK. Which will have the biggest impact on your visit, the easy walk to the MK or the less ideal monorail to Epcot?
The Poly does have an easy walk to the TTC in order to take the Epcot monorail. The Poly would also require an elevator to get to the monorail stop. The difference is that it isn't just the one tiny elevator at the Poly. You would have to take a monorail from the Poly to both Epcot and the MK. NO, wait! Or you could walk to the TTC and take the large ferry over to the MK.
The GF has a single elevator to the monorail level as well, but it is larger and doesn't seem as congested as the one at the CR. The Gf would be the least convenient option for transportation, IMO, as you would need to take the monorail to both the MK and Epcot.
I would choose either the Poly or the CR. My first choice would be a CR GW room with a request for the ground floor. However, TBH, I would go to Epcot infrequently compared to the other theme parks. YMMV.
Good luck! These are all really nice resorts! The three MK resorts are our favourites!