Tile or concrete would be the best, but you need to make sure that you reinforce the floor before installing a hot tub. Not only does the floor have to support your weight and the weight of the tub, but the water as well. You may want to sister the floor joists and put another layer of subflooring if there is living space below. If it's on a first floor resting on the foundation, have at it and enjoy.
this is totally not likely that your floor would desire to hold the load until you're on the basement floor on concrete. you may opt to seek for suggestion from with an engineer or architect to be certain in the experience that your floor would desire to be strengthened to handle the nice and cozy tub. through fact the nice and cozy tub is oftentimes saved packed with water, this places a protracted-time era weight and rigidity on the floor plus you've got the load of the nice and cozy tub occupants, the chemical compounds and water weight to deliberate to boot.
Do you mean under the tub or around it? Concrete and tile are my suggestions.
I would suggest tile but textured or pitted so it's not so slick. Anything shiny and glazed would be slippery when wet.