As others have said, living in base is HUGE. SKW is certainly a good place to do that since they don't always burn reserves at both ends (like some places) and when you get a line you can manipulate it to suit yourself, and there are a lot of good work rules.

Several other regionals would certainly offer good QOL in base too. If you're free and willing to move, then look at the bases for SKW, CZ, XJT, air whiskey, and horizon. I would guess movement/upgrade opportunity would be in this order: CZ, SKW, XJT, horizon. Not sure about air whiskey, probably not much opportunity but better than horizon.

IMO upgrade and QOL are not totally un-related unless you're independently wealthy. Upgrade means more dough which helps QOL, as well as enhancing your upward mobility which is really the best thing you can do for QOL in the long run.

You might consider mesa, psa, or endeavor if you're a career-oriented gambling man looking for a fast upgrade. They'll treat you like crap but living in base might take the edge off that and upgrades should come quickly if they can somehow actually staff all the new planes they're supposed to be getting. But if the music stops and you get stuck for years as an FO at one of those places you'll wish you'd never been born (or wish you'd been sold into sex slavery in SE asia shortly after birth).