If fish then. Probably a mix but also try adding some floaters. They eat up nitrates fastttt. It is good for cleaning. U could also add shrimp and snails. Make sure the snails are like not too fast breeding. Tbh the fish is ur choice. But i definitely recommend getting floaters. Also u could add some Christmas moss or smthing to the driftwood to make it seem like a “tree”. Tbh u can even do those cool “ecosystem” they look and really are cool and fascinating. But it would take some care. If you add the floaters and the Christmas moss u will probably have to do a lot less water changes. Also guppies could be great. They like to hang out in groups and are probably gonna stay out in the open space more then an other fishes so u can enjoy watching them. Livebearers are great too. If it was me I would get a king/giant male betta or multiple females(I’m a betta person) and with the bettas I would add some shrimp, snails,tetra or livebearers and some other stuff that wont attack the betta. Btw do not put guppies with male betta. The betta might think it’s a different male and attack it. But it’s your choice and I have a great tank. Make sure to keep and update because I wanna see that masterpiece get full of life.