Of those 4 I would consider Envoy the most serious. While far from perfect, I think it would provide you with the best opportunity as of right now.

Mesa has awful pay and will likely stagnate in the near future as their aircraft deliveries drop off and upgrades slow to a trickle.

TSA has been having difficulty filling classes and I think I read that they are not taking all of the originally slated 145 deliveries?

GoJet just upped first year pay but they got rid of their new hire bonus (to my understanding) which means you will make the same as almost anywhere else right now when you take that bonus out of the equation. Unless you live in STL I wouldn't really consider them.