If you are wanting the full spa experience, you currently have 2 choices on property. The SSR spa, which is currently operated by Niki Bryant spas, and the Mandara spa at the Dolphin. The GF spa, which used to be operated by Niki Bryant, has been closed for refurbishment for some time and will re-open, operated by Disney. The same is supposed to be happening to the SSR spa.
I've been to all 3. At this point in time, I'd probably choose the Mandara.