CichlidFish.com - Fish That Think.

Well Oscars are cichlids, and so are Angelfish... But they a basically not compatible.
First rule of keeping Oscars, nothing long finned and slow, and nothing that even looks small enough to fit in it's mouth So the goldfish are toast, probably the angel, maybe the gourami (depends on the species), a big Oscar could eat a rainbow shark etc.
Suitable tankmates are large plecocostomus (sucker fsih), well grown bala sharks, kissing gourami etc. All those fish can, like the Oscar, grow to a foot long, so you need some serious space. Start with 75gal for the Oscar alone, and then allow more for the other fish.
As for "Cichlids", there is a huge range, from about 1" long to 3ft. All sorts of temperaments.as well. Some are much bigger and way more aggressive than Oscars, others are little community fish.

Yea, I guess that's a trick question!?
But I guess many would say Oscars are the smartest cichlid, some would say they have their match with some other cichlids.
For sure its a lot of fun feeding oscars when they wag their tails like little puppies when they see you

I had an albino tiger oscar who loved to play on the water jets, laying on his side on top of the jet shooting out of the pump at the bottom of tank as the water pushed him all the way to the surface of the water, then right away he'd swim down and ride the slide again

I chose not really. I want to know what the majority of people choose.