I've been coming to True Rest for years (before the moved to Tempe), and I cannot speak True Rest's praises enough. It is an oasis of tranquility in my busy life. I've brought my friends and family (including my 71-year old father) here, and they are always astounded with how they feel afterwards.
The staff is always friendly, the rooms clean and stocked with that you need, and spa itself is comfortable. I highly recommend a membership, as you will really want to do this more than once to get the whole understanding of how floating works and how you can feel with multiple float sessions. Not every float may be transcendent (although the more you do it, the greater the chances of that happening in each session increase), but you will always get something out of it.