I think they are both the same as far as (out in the open fish) are concerned, i've found jd's and jags, come out in the open, and hide just as much . I, myself have seen no difference in the two. Jags are, in my opinion just more territorial, and like to bully other fish. They are more of a brawler, that's all. Both are very hardy, solid decent looking fish, but its hard to tell if either are actually interactive with their owners or just hungry. I've had both in the same sized tank, at different times, and i've noticed myself, that the jack was more an out in the open swimmer, and the jag was much more to himself, hiding just waiting for food to come to make a move. unless, of course if other fish were present, then he would make it known that he was king and would not let them make a move.