Depends on whether or not you're doing an LTC challenge or anything similar. Other than that, a few of them tend to be terrible due to low growths, and sometimes low base stats as well. Sothe and Titania are actually good in Radiant Dawn (they have great base stats too), and definitely usable because of the implementation of a 3rd tier, but Titania is only decent in PoR (not awful statwise like a true Jeigan) and Fredrick can become as good as most other characters because of the limitless reclassing. Seth managed to keep up fairly well on my second Sacred Stones play, so I can't call him bad. Jagen is just absolutely horrid. His base stats are nothing special, his growths are simply laughable, nor is he versatile in any way because of the lack of rescuing in the Archanea series. You can use him to weaken enemies in the max difficulty to help everyone else, but that's about it. I'm not far enough in Holy War to say anything about Oifey yet. Arran is sadly the same. As for Marcus, he's basically the prime example of a jeigan from the first part of my comment. Statwise, he's just super weak in FE6.