Without looking anything up, I would say colonial. The fact that the growth of the coenosteum/costae/wall makes the coral appear to be one large "polyp" is misleading. I would consider the fact that they have multiple mouths/gastrodermis to be an indication of a colony. But, maybe the mouths have to be in completely seperate skeletons such as Euphyllia.
This is interesting, I want to look into this. Lobophyllia would be another interesting study because of the differences in costae between it and Tracyphyllia.
What do you think, Scott?