They all have some play depending on your list, the old blood is a fantastic support piece in coalesced who can put out some good damage himself as well as doing dual command abilities. The scar vet is a slightly better monster killer at the cost of losing the 2x command ability. The trog is good in starborne, he recently got nerfed in that you can only cast one spell through him per turn but that can be usefully to get an important buff spell off on a far away squad and his aura and spell are pretty useful. I primarily play coalesced and almost always bring the old blood myself but all 3 have some potential play.
