1. Toadstool Mushroom 2. Candy cane coral 3. Zoanthids 4. Xenia, but it can grow where you don’t want it to grow 5. Red Cap Montipora for those who want to try SPS
That's a tough one... For softies obviously zoanthids but there's a huge assortment. I'd also go with a nice bright green nepthea as they don't drop babies everywhere and seem fairly hardy. Then there's GSP as long as you manage it correctly for SPS pink bird's nest and some of the basic Montis.
Would be easier if we could break it down by three top as SPS, LPS, Etc.
@MERKEY Has the right idea. I passively didn't do anything to my tank for nearly a year and most of these corals listed are the ones that survived. Hell even a few thrived (GSP).
Truly recommend though if you get these 'starter' corals to put them on their own islands as most of them are pretty invasive in terms of growth and removability.
The tiny frogspawn and hammer frags we got WAY back with our first tank have been fragged off over and over again. Once as a gift to a friend, plus several large colonies to an LFS for fantastic store credit. Definitely good choices - so many others have never thrived so well.
Easy corals that will not take over your tank right away
Mushrooms Anemone Coral like (Actinodiscus cardinalis)
Cabbage Leather Coral (Sinularia dura)
Green Toadstool Mushroom Leather Coral (Sarcophyton sp.)
Candy Cane Coral (Caulastrea furcata)
Zoanthids (Zoanthus sp.)