I have no experience with Pepperhead at all. I have no direct experience with Pepperjoe, but I have been told by multiple sources that the business ain't what it used to be. And that the seeds growing true is a crap shoot. But, like I said, I have nothing empirical to add. Maybe Pepperjoe is rad and I've just heard some negative rumors...
Now, I have ordered both pods and seeds from Peppersbymail. Repeat customer here, and I will definitely order again. Product was great, but more important to me, the owner is THP's own AJDrew. If you're not familiar, AJDrew is extremely active here. He is always willing to give advice, offer insight, etc... And, even in the dead of the North American off season when traffic on THP slows down, he tries to keep the discussion going by posting a lot of threads looking for other growers' opinions and perspectives on various chile topics. I seem to recall ordering seeds from him because he was doing something charitable with the proceeds--I forget the details--but I wanted to support that, and when I got the seeds, he'd tossed in some generous freebies and a handwritten note.
Like I said, I never ordered from the other two outfits, and maybe they're great. I'll let the other members weigh in on those. But peppersbymail offers good seeds at great prices, & fast shipping if they're not snowed-in... And your order will support a family owned and run business, headed up by a guy who is truly dedicated to the Chile Lifestyle. I don't know if that means a lot to you, but it matters to me. Which is why I can't say enough good shit about the business.
Good luck...