Hi. I would recommend the GF Spa. It also happens to be the only one on your list that I've been to. But I have been there a LOT
One thing that would influence me, though, is my resort choice. Where will you be staying? If you're staying at SSR then I would go to their spa. (Also, it is a newer facility and I have heard great things about it

) If you're staying at any of the Epcot resorts I would say go ahead and enjoy the Mandara spa. (I have heard really rave reviews of it as well.)
If you're staying at the Poly or GF, by all means enjoy your treatments over at the GF Spa. For starters, you can walk over! Also, I have always, always had very good massage therapists and nail techs there. I have had one facial and it was EXCELLENT. That was back when they used Jurlique products, which I adore

I have had a body scrub that was nice. Never had any of the water therapies.. But for massage it is great. It's a nice-sized facility. The lounge is nice and the showers and bathroom area were recently refurbished. The spa is definitely pricey but if you're a Passholder you get 10% one treatment per visit.
I don't think you can go wrong with any of the 3 you've listed. Good luck!
