I had sugar sand in my nano something I regretted due to how much it got blown around in such a small system.

I helped a friend setup a 25 gallon and I liked what he did which was put course sand down over two thirds of the tank to about an inch deep and then put crushed coral down in the other section to same depth however the downside was the sand eventually mixed in and spoiled the look but according to him his gobies loved sitting on the crushed coral during the day

I think if it was done right it could look good in a nano system sand and crush mix I know I like it In my big tank

I'm a travertine tile fan. Clean and doesn't look as crappy as BB

If you want to go bare bottom another option is to use "Starboard" aka HDPE plastic aka cutting board material. Most plastic/acrylic shops carry it and it's not expensive. You can order it in 1/4" or 1/2". It floats and silicone won't stick to it well enough to hold it down, so you have to put rock on top to hold it down. Looks great. Do some Google Image searching for "HDPE BB reef".

yeah! that looks pretty awesome! I might try the cutting board material.