Bafanguy says Fed-Ex and UPS are destinations and not steppingstones.
Atlas, Polar, Southern, National, Centurion, Kalitta Western Global etc, etc should be your stepping stones to these destinations.
Zondaracer wrote an excellent article about the regionals.
The problem with being happy at Horizon or Skywest is you may like it and stay. A kid from my town ended up married with four kids and a mortgage in Seattle and forgot to leave. Still talks about joining Alaska but does nothing about it. Sometimes the worst regional is the best in the long run. Get in, get some time and get out.