This topic is all over with pros and cons from everywhere.
I myself have always been a fan of sand. It looks great. I won't say it looks "natural", due to the fact that if you look at the reefs in the ocean, you don't see sand. You see huge mountains of rock, with coral.
While sand looks great, I removed it all at once from my old 75 SPS Dominant tank. I had a thin layer so it didn't effect anything. Though I was able to up my flow quite a bit and feed more without effecting my parameters. I was able to keep the tank spotless. At this point I actually had an outbreak of coraline.. Yes, an outbreak. I had to clean it off weekly lol. My tank was thriving, corals wouldn't stop growing. I was running Reefbreeder LEDs. I could only imagine what I would have experienced running T5's like I am now
All in all, barebottom is great. Massive flow, gives it a deep color in the tank, thus allowing corals to 'pop' more.
Though sand also looks incredible.
I say, if you do sand, do a thin layer. It won't be much of an issue to water parameters, if at all. Though the only downfall would be flow, as it would have to be turned down a bit.
When it comes down to it, either way you will be successful.
Maybe go BB and if you don't like it, add sand later? That's always an option as well.