Curb Side Freebie - What to Stock

I found a ~20 gallon set up out on the curb. Tank holds water and all the equipment works. I guess someone got tired of the hobby. Found a place to put it and now I want to get it going. But I can't decorate until I have some stock in mind.

Shelldwellers/Tangs (vals, anubias, java ferns with fine gravel and cool shells)

vs.

Planted community (black substrate with dark green plants and driftwood/rocks)

vs.

???

Which would you do?

Thanks, that's helpful. But which substrate? It depends on the stock. Which one do you prefer?

It's not a standard 20. I need to find a ruler and measure it and convert it into liters, but it's more of a high than a long Which is a bummer. I've noticed the tall tanks tend to be favored here (south Korea).

I've never kept shellies, but it seems like a colony of multis or occies would be the way to go I know there is one store at the pet market that has tang cichlids, so I will pay them a visit to check out the prices and species!

Well, after following the prescribed advice about water (I was going to fill it with soju but I figured drunk fish weren't the best idea), the tank is somewhere between 15-20 gallons.

I went to the store and looked at the shellies... fell in love with the pearly occies... did some research and am crushed. Sounds like they're too aggressive to house in my tank. Looked at the multis too and they just don't do it for me Going to go with a pair of dwarf S. America cichlids instead with a planted tank and driftwood. I picked up a nice, intricate piece for $15.