How much flow do you have? If you have the right conditions most of them can be placed in the easy to keep category - just avoid non-photosynthetic corals such as Carnation corals.
For the firm fleshed soft corals such as Sarcophyton and Lobophytum sp. (Toadstool corals), high flow makes keeping them a lot easier.
For the very soft fleshed soft corals that can easily sway such as Kylxum (Colt coral) and Sinularia, medium flow.
And for morphs, low flow.