I agree, soft corals seem to be fine, though they do generate more "stuff" in the water--mucus, terpenes, etc. I have Green Star Polyps that have produced a fabulous, luxurious carpet along my liverock, and they are just plain delightful.
I've also had surprising luck with Large Polyp Stony corals (LPS.) Not entirely sure why. They're more likely to sting (I believe one has stung me) but my octo never had a problem with them. They're also supposed to be harder to keep alive, yet again, mine are thriving. Theories on that:
I have both a Trachyphyllia sp. (open brain coral) and a Catalaphyllia jardinei (Elegance coral.) Especially in the case of the Elegance, I bought before I researched
and later learned of the difficulties with these, including concerns about overharvesting from the wild...
Elegances are reputedly quite "touchy." MANY aquarists have had them die horrible deaths, and sworn them off. There is some thinking now that this may be because they corals were being given traditional reefkeeping conditions--high light, high current, ultra-clean water--when in fact their natural habitats were low-light, low-current, silty seabeds. Mine have been on the bed of my tank in low current pretty much since introduction, and seem quite happy with that (also seem quite sensitive to salinity fluctuations, fyi.)
So you might be able to use these corals, but they may be very hard to keep (my experiences seem to be quite atypical) and they may be overcollected from the wild anyway. :?