Talk about a hard topic. I’ve always thought it would be African Cichlids, but I’ve come to realize that I’ve had one type of fish that has been in ALL my freshwater tanks. If they can go in saltwater, I would have put them in there as well.
Endlers livebearers.
I’ve had them in my 10s and 20s with shrimp and corys. I’ve had them thrive in my 60 gallon jungle tank with female bettas and an angel fish. I have them in my pond right now, with goldfish, whiteclouds, and guppies. I have to admit that when the population is too much, some have gone in my African cichlid tank. They serve as a snack there, but I think that counts too.