depends on the size of your tank but i have Oscars they get really big and they are fun to watch when they eat goldfish, also my friend has red belly piranhas and they are also fun to watch.
I agree that Oscars are interesting fish but as mentioned, they're big. No one mentioned how big though so I will.
The grow 12-14 inches big and you need a bare minimum of 55 gallons for 1 fish. And feeding them goldfish is bad =( It could give them hole-in-the-head.
I would suggest that you get a smaller cichlid like convict cichlids. They don't get near as big as an oscar and you can house 1 in a 25 gallon tank.
Or if you were to get a slightly bigger tank, 30 gallons, then you can get 1 or 2 angelfish. They are beautiful to look at and they're cichlids too, like the oscar and the convict.
Or if you want, you can go with a 20 gallon tank and get a fancy goldfish. I never owned one but I heard that goldfish can have nice personalities.
Get six tetras, I have black skirt tetras and they are hilarious!
I love to watch them, they all follow each other and do the same thing.
Feeding them is funny too.