I only know about Eagle and I have heard some horror stories about how junior pilots are treated there. I have also heard that Chautauqua is a good regional to fly for. Eventhough Mesa might be tempting because of their large operation I would stay away because pilots say that it's not a good place to work, just to gain experience and move on. Bottom line, if you want to go to the majors then it really doesn't matter what regional you go through as long as they have good upgrade times. If you want to stay at the regionals then follow what I told you above.