BW hands down my favorite. I have stayed at both and while the GF was beautiful, the BW was just more for me.
The rooms at the GF are in separate buildings. We had the building at the far end of the resort, so it was a little out of the way from everything. After staying at many of the Disney properties I find myself liking the hotels (like BW & WL) where you don't have to walk outside to get to your room. The grounds were beautiful and the service was great. I am glad I stayed there once, but I am in no hurry to rush back there.
With the BW I am the complete opposite, I can't get enough of it! Every resort I stay at while in Disney I keep comparing it to the BW. There is something about it that is magical. I love the whole theme and the ambiance is wonderful. I love waking up in the morning and stepping out on the balcony and seeing the boats go by and hearing the boardwalk music play while I eat my breakfast out there. I like to "people watch" so for me it is the perfect place to stay. I always get the room that is on the boardwalk so I can open my door and be right where all the action is. It is great at night...tons of things to do. Every trip I make sure I set one night aside to just do the Boardwalk activities. I will wake up early in the morning and jog a few laps around the Boardwalk, get my exercise in and take in the beauty of the resort. To me it is the perfect place to stay.