it is funny that you should ask this question, my friend and I have had this same conversation so we set up a few tanks
1) 55 gal Natural Gravel dwarf Cichlid
2) 72 gal zoo something (like dirt) schools of diff tetras
3) 110 gal filter sand fire eel and cat fish
4) 10 gal reg. sand (from lps) guppy, snail & shrimp
5) 35 gal Oil Dry puffer
6) 12 gal Nano Salt tank coral sand
7) coming next 29 gal will have a different kind of dirt and sand base
all are live planted tanks, all have diff. light systems from T12 Aquadic, T8 Aquadic, T5 sun & autinic, T5 sun blast, then halogens

it is a good thing they are in diff. houses or the whole street would go dim when we turn the lights and air on in the Morning

we just got together this weekend and talked about how thing are going with the diff. substrates
you should always consider what fish you will be putting in the tank, the oil dry is awesome for plants and the roots... however I could see my fire eel sending that stuff right up the filter it is so light, the dirts are very nice plants seem to do great in it however if you have a fish that tears things up you will never be able to see inside the tank..... Now sand either kind seems to be a steady substrate it does not get as dirty as the gravel in the lower levels, it always looks great and will not hurt the fish (that we have) and for the fish that like to toss the substrate around sand does not go up very far and comes down quick.... the down side is that vacuuming can be daunting, if you push down into it like you would on gravel it goes out the tube very fast

yes I have nice sand in my flower bead where I drain the tank for water changes.... Gravel is always a good stand by easy to keep, easy to clean can hurt your live plant roots and fish that like to bury themselves..
not an expert by any means just sharing how our little science project has been going.... and boy has it been a chore,
also another thing to keep in mind is how soon do you want to add fish after you add your substrate

some of our tanks have taken up to 1 (one) month to settle down