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If you're installing a floor in the space concrete over the plastic vapor barrier would be best. In this case you shouldn't need/don't want another vapor barrier on the bottom of the floor joists. You could use plywood on the bottom of the joists.
You can't put anything on the floor that won't destroy (poke a lot of holes in) the plastic. Only concrete will give you a good hard surface and protect the vapor barrier. With a vapor barrier on the floor you don't need one on the ceiling and would be better off without one which could trap moisture in the joist space. You could use a product like Tyvek which would allow water vapor to pass through it.