So many people say that healers use tank companions. I must be odd. I use Temple with my Operative and Andronikus with my Sorcerer. I end up "tanking" while they tear the mobs apart. I find it easier to heal myself than it is to heal them,
The companions I never see are Scorpio and Dr. Lokin. But I don't pay a lot of attention to other peoples' companions.
I use Akaavi almost constantly with my Sawbones and have never regretted it. And I managed to persuade a friend to use Yuun with his Combat Medic, who he's now very pleased with. I'm always surprised how few of either I see around the Fleet or on planets. I almost never see either.