I have no carrier that is "it" for me at this point, but I've started to aim for Southwest.
My Dad was a mechanic for Usairways starting back in the Allegheny days. I was an airplane cleaner (Line Maintenance Utility in Usair speak) for two years in the early 2000's until being laid-off. So I'd be lying if I said flying for USAmericanWesTWAys didn't hold some allure for me. There's a lot of opportunity in terms of equipment and routes. And Americans soon to be retired shiny airplanes have always been cool to me.
But it seems no one is happy there and I understand why to a degree. My Dad had his pay and more importantly, his pension slashed by the multiple bankruptcies at Airways. QOL took a nosedive for all parties during the multiple bankruptcies and realignments. When I was a lowly utility person in PIT, there were still people pissed about the late 80's Piedmont/USAir merger in every position. Add in the whole America West merger, American merger and there's probably a fair amount of animosity between groups. You can apply this to any legacy carrier, true, but the corporate culture at Airways was one of "everyone for themselves". I can't see how the changes that have occurred since I long left the company would have improved on this.
My regional flies for United only and has a CPP program with United. I'd love to fly for United, but I don't find them to be very customer friendly. And the CAL/UAL merger still hasn't worked out its bugs either, thanks in part to Jeff Smizeks "quest for cash" managment style. United has nearly the same offerings for fleet and routes as American.
Southwest, according to a friend who want there from my regional, is more like a regional airline, but with better pay,equipment, QOL and such. And I've jumpseated on Southwest as well as been a paying customer a few times. Southwest offers a decent product and I've never really witnessed any totally grumpy Southwest folks. Call it the Southwest effect or call it BS, people seem happy to be there. And as much as I would like to be paid to fly all over the world, I'll take the relative stability and level of happiness over that.