We just got back and I had a gardenview room booked. However, upon check-in, we were given a complimentary lagoon view room (not sure why but it made us very happy!). We were in Big Pine Key. This building is great if you will be spending a good amount of time in the themed pool as this building kind of sits between the two pools. It is also close to the entrance to the main building. This comes in handy when it's storming out!
However, if pools aren't a big deal for you and you will get better use of the marina and want to be close to the food and arcade court (for refillable mug refills), I think Sago Cay, Boca Chica or Conch Key would be a good option (a bit less of a walk). I was suprised at how close Sago Cay was to the food court because all of the maps I have seen make it seem like it's off to the left a bit. Actually, all the buildings are fairly close together so where ever you end up shouldn't be too bad of a location.
If I could make a suggestion. All the buildings have thier own little lobby and it goes floor to ceiling. I found the lobby at Big Pine Key could get a little loud at times when people were coming and going, waiting for the elevator etc. (especially on the first floor). Voices seem to travel. If you think this will bother you, you may want to ask to be put on
either side of the building, not in the lobby. We were on a wing and it was very quiet.
You are going to love GF...it is a beautiful resort. Enjoy!