We have done the tea at the GF several times and love it. We plan on doing it again in the future.
There were a couple of things that swayed me in the direction of having it through DFTW.
The first was timing. The Gardenview Tea Room doesn't open until 2pm. We have our welcome dinner planned for 6pm that evening and I wanted to give the ladies plenty of time to get hungry for that. Our early event will be over by 2, so if people want a few hours in the parks in between they can have it.
We also wanted it to be convenient. All of our events are in Epcot or at one of the Ecpot resorts and we think that most of our guests are going to stay at the Beach Club. If we had held it at the GF, I would have felt obligated to provide transportation to and from, since most of my guests wouldn't know their way around. Also, if guests are just arriving that morning at the hotel, they just have a short walk to get to the luncheon.
Not sure what your full schedule is or your locations, but wanted to present another angle.