We stay at both...meaning one year GF the next Poly. They are both my favouirtes and are different but equal, IMHO. When staying at the GF we stay in the consierge dlx rooms in the main building. I love the cons level of the GF and we find, although the rooms may cost more, we actually wind up spending less money when we stay there (when all totaled at end of trip). The rooms are beautiful and we love staying in the main building, it is very convenient. Also we find the Cons level to be much more quiet. You know how beautiful the lobby is and we love having dinner at Citricos, then going to the bar in the lobby, listen to music and have a night cap, then ride the elevator right up to the room (no walking!) We also love the shops in the GF and the whole feel of the place - it certainly is Grand!
When we stay at the Poly, we always stay in the Tahiti, on the ground floor. The beach is beautiful at night, lit torches, hammocks, a beautiful view of the Castle and fireworks and the lagoon parade. All right from your patio.....that's why we love the ground floor - just walk right out and theres a hammock and beach chairs, its very lovely. Also the Poly is the closest to the TCC which you can walk to as there is a path right from the Tahiti directly to the TCC (or if you are going to the MK just walk to the Main House and get it from there). If you want to go directly to Epcot, you do not have to ride the monorail all the way around, which saves a lot of time. I guess it is a matter of preference, the Poly is to me "Old Time Disney Magic" and the GF is "Upscale Disney". Both are unique, relaxed and beautiful and we have a hard time deciding which one is our fav, so every year we switch off