For LPS corals, I find the Euphyllia sp. (hammer, torch, frogspawn, grape, anchor) pretty hardy and under good conditions can grow reasonably fast. I'd say the hardiest of the LPS would be the large button polyps - Palythoa & Protopalythoa sp. Many zoanthids are pretty hardy too.
Most SPS prefer very stable & consistant water parameters - with minimal variations in ANY property. Even minor swings can cause problems. But I have found a couple hardy (&forgiving) sps that are fast growing.. Seriatopora guttatus - orange guttatus birdsnest; S. hystrix - pink birdsnest; Most of the Montipora sp. are pretty hardy. I bought a Sprung's Stunner Echinopora ORA frag from this site - and it's the fastest growing encrusting coral I've ever seen, adding 1/2"+ per month of new growth. It was 2" diameter in March '11 and today it's over 7". Sadly most of the Acropora sp. are pretty sensitive, and should not be the first SPS frags someone attempts. Acro also has a need for a very established tank - 9-12 months minimun, and many people who attempt keeping acro in a new tank watch it die off rather quickly.
