After 45 years, it varies. My first criteria is that it is easy to tale care of. Chilli Coral is an exception to that rule. The second criteria is that it is either pretty or interesting. Third criteria is that it gets along with tank mates. To this point there is a kind of social order to be dealt with.. With LPS coral, you can move them out of sweeper tentacles range or in the case of noxious chemicals from softies being removed with GAC.
Fish are more difficult. Once they are in the tank, it is difficult to effect their behavior.