I would say most birdsnest grow like weeds under the right conditions. Plating and branching montipora seem to grow very quickly as well, ie. M. digitata and capricornis. Some people have excellent growth out of the encrusting montipora as well. Personally I find the sunset Montipora to grow very fast out of them. As far as acros go, most stags grow pretty quickly especially the green slimer (a. yongei). I have always found a. millepora/prostrata/hyacinthus to grow very quickly as well.