I like the natural look of the substrate / sand. It allows me to simulate the small piece of the living sea / ocean. Reminds me of the times I go snorkeling.
One tank sand, the other tank is no sand. All depends on the tank.
So... Do you have any issues controlling water parameters with the no sand tank? This is a concern as I have heard having substrate has a buffering capability. Of course... I think that can be offset with the ability to export waste out of the system more efficiently....