I keep both. My bare tank just has an 1" of gravel nothing else just lots of big fish. I'd like decor and have had it in there in the past when the fish were smaller. Now its all about the fish giving them all the swimming space possible without obstructions until they get a bigger home.
Abit of both... But ultimately It's all about the fish. I have a few set-ups that are "Ghetto"... But the water quality is perfect and the fish have plenty of room until I can dump money into something "Nicer" looking.
It all depends on what you are doing with your fishes. When I kept fishes for fun and watching, then my tank was decorated and had lots of gravel and rocks.
Now I only have breeders and so my tank is bare, except for the few grains of gravel I couldnt get when I cleared out the decors/gravels. Breeders HATE gravels...my Red Tiger pair pushed all the gravel up against the tank about 3-4" high. The tank looked Stupid so I got rid of the gravel.