+1 Montipora digitata. Purple stylo is one of the hardiest stoney corals I've come across including soft corals and polyps. The birdsnest are pretty hardy also.
This doesn't seem to get much attention but keep in mind many corals may need very specific tankmates. The confusion over keeping Goniopora is one example with ~22 species and no way to distinguish between species but only a couple with wide distribution indicating adaptability and most only found in specific ecological niches. Now with cultured specimens aquarists are seeing much better overall success. This article on Acropora microladoas, strawberry shortcake, is another good example with only a small percentage of colonies found in the company of other species besides acros
This doesn't seem to get much attention but keep in mind many corals may need very specific tankmates. The confusion over keeping Goniopora is one example with ~22 species and no way to distinguish between species but only a couple with wide distribution indicating adaptability and most only found in specific ecological niches. Now with cultured specimens aquarists are seeing much better overall success. This article on Acropora microladoas, strawberry shortcake, is another good example with only a small percentage of colonies found in the company of other species besides acros