undulated, we have had both in the same tank, they got along well for some reason but every once in a while we would give them goldfish, and not those tiny feeders, the bigger two three inch ones. The undulated was about two inches and the clown trigger was about 6 inches, when the goldfish hit the water, the clown didnt seem to notice right away, but the undulated when right after them and went for the eyes first, the when the eyes were plucked out of its head, it would finish the fish off. The clown seemed to be less gory about it.
Heres a good one, what would win, a beta fish or a goldfish(both the same size)