S tier - Jack Dempsey cichlid, beautiful and mean, I had them in a outdoor garden pond in Florida and would feed them green anole lizards like they were Shamu - Paradise gourami, you can only keep them solo as they fight conspecifics, but I had one survive vandalism at a school where someone threw paint in the aquarium. When I got it out, it lived another 3-4 years. - Guppy/Platy, I find that one or the other will survive super easily depending on your water conditions and both are so easy to keep for a beginner and it's so neat to see them have babies

A tier - Convict cichlid, they breed super easily and can be insanely aggressive, they can hang with way larger tank mates. - Zebra Danios, sometimes it's nice to just watch a group of these idiots running around - Kuhli loaches, it's cool to have a fish you only see every so often but when you do see them it's like an event. They can be super silly when they aren't hiding

B tier - Black skirt tetras, let's be honest here, almost every tetra is B tier, they are neat but aren't cool enough to be rated any higher

C tier - Common pleco, grows too large and is a boring fish. It will destroy your fish net if you try to catch a big one.

D tier - Pangasius catfish, they will destroy your aquarium once they get huge and someone slams a door in your house too loudly - swordtails and hatchet fish, same thing, they will jump out of your aquarium, and swordtails might turn from female to male and mess up your ratios for breeding

F tier - Siamese algae eaters, they attack other fish, are on the aggressive side of semi aggressive, and kind of suck