^^ so it's really up to you and your personal tastes. Bare bottom tanks allow greater flow, and less maintenance, but you'll lose out on the biodiversity a sand bed can provide. If done properly, you'll have happy sps.
A shallow sand bed restricts you from having a huge amount of flow, but a high flow rate is possible. However, it allows for greater biodiversity. It gives amphipods, copepods, tiny starfish, sea cucumbers, serpent stars, burrowing fish like jawfish and some wrasses, and many other creatures a place to live. If done properly it can give you happy sps.
And a deep sand bed restricts your flow potential more, although high flow rates are still attainable with care. It provides an even greater habitat for more creatures to inhabit your tank, and acts as a buffer to some of your chemical properties. It will lower the total water volume of the tank though, meaning you have to be a little more careful dosing wise. But it's negligible how much it will matter. It can also be a ticking time bomb for your chemistry if not taken care of properly. If done properly you'll have happy sps.
So it's up to you. All three are fine and can make for happy sps. But what kind of reefer are you? Are you all for maximum sps growth and ease of care? Go bare bottom. Are you all for maximum biodiversity and don't mind a extra tank maintenance? Go for a deep sand bed. Or are you in the middle? Go for a shallow sand bed.
I personally love seeing as much life in my tank as possible while not risking a tank meltdown by disturbing a deep sand bed. So I've gone with a shallow sand bed. Throughout a year period, I siphon a little out during water changes. And replace it with new sand as need be. So my sand bed never really sits long enough for bad stuff to collect and probably is totally replaced inadvertently each year.