I think K Charters II only hire captains who are rated...at least that was how it was before...

USA Jet and Ameristar are similar operations, but in different locations. At USAJet you can start as FO, get training, and work your way up to Capt. You can start as a -135 FO on the Falcon 20, if you don't want to wait for your ATP.

I think Everets is probably the best, overall, for most pilots.

Also, K Charters II: you normally can't move from there to Kalitta Air, if that is a consideration.